Bones Of The Skull Mandible

The mandible is the bone of the lower jaw.

General Features of Mandible Body

Mandible Body

The body is U-shaped and has two surfaces and two borders. It consists of right and left halves united in the median plane at the symphysis menti. The symphysis menti is a faint ridge on the upper part of the midline.

Mandible Body Upper Border

The upper border of the mandible is also known as alveolar border. It bears sockets for the teeth.

Mandible Body Lower Border

• This border is also known as the base of the mandible. Posteriorly it is continuous with the lower border of the ramus of the mandible.
• On either side of the midline, there is the presence of a digastric fossa for the attachment of the anterior belly of the digastric.

Mandible Body External Surface

• At the lower part of the midline (at symphysis menti) a triangular mental protuberance is present.
• The upper angle of the triangle lies at the lower end of the symphysis menti.
• The mental tubercles are present at the lower angles of this triangle.
• A faint ridge is present on the external surface of the body extending upwards and backward from the mental tubercle up to the anterior margin of the ramus. This is called an oblique line.
• The mental foramen, in an adult, is present below the second premolar tooth midway between the upper and lower borders.

Mandible Body Internal Surface

• The mylohyoid line is oblique and extends diagonally downwards and forwards from just below the alveolar border (behind the 3rd molar tooth) to the lower part of symphysis menti.
• The sublingual fossa is a smooth area above the anterior part of the mylohyoid line for the lodgement of the sublingual salivary gland.
• The submandibular fossa is a concave area present below the posterior part of the mylohyoid line. It comes in contact with the superficial part of the submandibular gland.
• The posterior part of the symphysis menti on either side of the midline presents a pair of elevations called superior and inferior genial tubercles. These tubercles are present above the anterior end of the mylohyoid line.

Read and Learn More Human Osteology Notes

Ramus of Mandible

The ramus of the mandible projects upwards from the posterior part of the body. It has four borders (anterior, posterior, upper, and lower), two surfaces (lateral and medial), and two processes (coronoid and condylar).

Ramus of Mandible Borders

• The upper border forms a notch, i.e., the mandibular notch. This border displays a triangular coronoid process anteriorly and a condylar process posteriorly.
• The lower border is the backward continuation of the base of the body of the mandible.
• The anterior border of the ramus is sharp and continuous below with the oblique line on the lateral surface of the body of the mandible.
• The posterior border meets with the lower border of the ramus to form the angle of the mandible. This border is in continuation above with the condylar process

Ramus of Mandible Processes

• The coronoid process is flat and triangular, which projects upwards from the anterosuperior part of the ramus. It lies at the junction of the upper (mandibular notch) and anterior border of the ramus.
• The condylar process projects upwards from the posterosuperior part of the ramus.
• The upper end of the condylar process is expanded and forms the head of the mandible. While the lower part of the condylar process is constricted and called the neck.
• The head of the mandible bears an articular surface that articulates with the mandibular fossa of the temporal bone to form the temporomandibular joint.
• The anterior surface of the neck shows a depression called pterygoid fovea for attachment of lateral pterygoid muscle.

Ramus of Mandible Surfaces

• The lateral surface is rough and flat in its anteroinferior part for the attachment of the masseter.
• The medial surface presents a mandibular foramen close to its center. It leads into a mandibular canal which opens at the mental foramen.
• The lingula is a tongue-shaped projection near the anterior margin of the mandibular foramen. There is the presence of a mylohoid groove just behind the lingula.
• This groove runs forward and downwards from the mandibular foramen to the inner surface of the body of the mandible.
• The area above the angle of the mandible is rough for the attachment of the medial pterygoid muscle.

Particular Features of Mandible Body

Attachments of muscles are shown for the external surface and internal surface. Relations of nerves, blood vessels, glands, and ligaments.

Mandible Body Ossification

• The part of the bone between the mental foramen and mandibular foramen ossifies in the membrane (fibrous envelop of the Meckel’s cartilage of the first branchial arch).
• The part of the body in front of the mental foramen and the part of the ramus above the mandibular foramen ossify in cartilage.
• Each half was replaced by a bony union at the end of the first year of postnatal mandible ossifying in 6th week of IUL.
• At birth, the mandible consists of two halves of the mandibular body united by the fibrous joint at symphysis menti. This fibrous joint is aged.

Age Changes In Mandible

The bony features of the mandible change with age (children, adults, and old age).

Frontal Bone

• The frontal bone forms most of the part of the anterior cranial fossa. The bone consists of squamous (main) parts and orbital parts.
• The squamous part forms the forehead and orbital parts form the major part of the roof of each orbit.

Frontal Bone Squamous (Main) Part

This part of the bone has an external surface and internal surface, right and left temporal surface, nasal part, and zygomatic processes.

Frontal Bone External Surface

• The external surface of the squamous part forms the forehead. This surface presents frontal eminence about 3 cm above the supraorbital margin.
• The other features seen on this surface are the glabella, superciliary arches, and supraorbital margins.
• The supraorbital notch or foramen is seen on the supraorbital margin. Occasionally the metopic suture may be seen in the region of the glabella.

Frontal Bone Temporal Surface

This forms a small surface on the right and left sides below the temporal lines

Frontal Bone Internal Surface

• This surface is concave and shows the impressions of cerebral sulci and gyri.
• It shows a median groove (sagittal sulcus) for the superior sagittal sinus.
• At the anterior end of the groove, there is the presence of a median ridge called the frontal crest. Just below the frontal crest is the presence of foramen caecum.

Frontal Bone Nasal Part

• The nasal part is the downward projection of the squamous part of bone between two superior orbital margins.
• The lower serrated margin of this part is concave downwards and known as the nasal notch.
• The nasal notch bears a median projection, the nasal spine which articulates with the nasal bones in front and behind with the perpendicular plate of the ethmoid.
• From medial to lateral, the nasal bone, frontal process of maxilla, and lacrimal bone articulate with each half of the nasal notch.

Zygomatic Process

The zygomatic process passes downwards and laterally from the lateral end of the superior orbital margin.

The Orbital Part

The orbital part consists of right and left orbital plates separated from each other by a wide notch called an ethmoid notch.

• The notch is occupied by the ethmoid bone.
• The orbital surface faces downwards. It is smooth and forms the roof of the orbit.
• The inferior aspect of the orbital plate, just lateral to a notch, shows the depressions of ethmoidal air cells. More anteriorly it shows the opening of the frontal air sinus.
• There is the presence of lacrimal fossa at its anterolateral angle.
• The trochlear fovea is present, at its anteromedial part.
• The upper surface of the orbital plate forms the floor of the anterior cranial fossa and shows the impressions for sulci and gyri.

Articulations of the Frontal Bone

The following bones articulate with the squamous part of the frontal bone:

• Posteriorly: Parietal bones (at the coronal suture), greater wings of the sphenoid.
• Anteriorly: Zygomatic bone, nasal bone, frontal process of maxilla, lacrimal bone, and perpendicular plate of the ethmoid.
• The following bones articulate with the orbital part:
• Posteriorly: Lesser wings of sphenoid.
• Medially: Orbital plate of ethmoid.

Frontal Bone Ossification

• It ossifies in the membrane.
• Two halves of the frontal bone begin to fuse at the age of the first post-natal year. The fusion is completed by the end of eight years.
• If the suture persists in adults then it is known as a metopic suture.

Parietal Bone

The parietal bones are quadrilateral in shape and form the roof and side walls of the cranial cavity.

Parietal Bones General Features

Each one has:

• Four borders: Superior, inferior, anterior and posterior.
• Two surfaces: External and internal.
• Four angles: Anterosuperior, anteroinferior, posterosuperior and posteroinferior.

The external surface is convex. The external surface shows the parietal eminence, parietal foramen, and superior and inferior temporal lines.

On the concave internal surface, the vascular grooves (for middle meningeal vessels) run upwards and backward from the anteroinferior angle. A shallow groove for the sigmoid sinus is seen at its posteroinferior angle.

Parietal Bones  Particular Features

The attachments and relations of the bone with the soft tissues

Parietal Bones  Articulations

Articulations of the parietal bone are shown in

Parietal Bones  Side Determination

Hold the bone in such a way that the convex external surface faces laterally. The angle showing the vascular groove at the internal surface should be kept antero-inferiorly.

Parietal Bones  Anatomical Position

The superior border should be kept towards the median plane, the antero-inferior angle downwards and forwards.

Parietal Bones  Ossification

It ossifies in the membrane

Parietal Bones Occipital Bone

• This bone is present in the posterior part of the skull. The presence of the large foramen magnum helps in dividing the bone into four parts.
• A part above and behind the foramen magnum is an expanded curved plate of bone, i.e., a squamous part. It shows a superior angle and two lateral angles.
• The superior angle lies at lambda and each lateral angle at asterion.
• A part in front of frame n magnum is called the basilar part.
• A pair of condylar parts are present on either side of the foramen magnum.

Parietal Bones Anatomical Position

Hold the bone in such a way that the foramen magnum should lie in the horizontal plane and the basilar part should be directed forwards and upwards.

Parietal Bones General Features

Squamous Part

• The squamous part shows a convex external and a concave internal surface: one superior angle two lateral angles and two borders i.e., lambdoid and mastoid borders.
• The external surface shows the presence of the external occipital protuberance and external
  occipital crest.
• The highest nuchal line and the superior nuchal line run laterally from the external occipital protuberance, on the right and left sides. The inferior nuchal line runs laterally from the middle of the external occipital crest.
• The internal surface of the squamous part shows the presence of internal occipital protuberance in the middle.
• A wide median groove for the superior sagittal sinus is present above the protuberance. Grooves for transverse sinuses are present on either side of the protuberance. An internal occipital crest runs downwards in the midline from the internal occipital protuberance.
• Borders—The lambdoid border articulates with the parietal bone at the lambdoid suture and the mastoid border articulates with the mastoid bone at the occipito¬ mastoid suture.

Basilar Part of the Occipital Bone

• It extends forward and upwards from the anterior margin of the foramen magnum. This part has three surfaces (anterior, superior, and inferior), and two lateral borders.
• The anterior surface extends upto the body of the sphenoid bone and forms a primary cartilaginous joint (basi-sphenoid joint), which is replaced by the bone at about 25 years of age.
• The superior surface slopes downwards and backward and forms a part of the clivus.
• The inferior surface bears a pharyngeal tubercle The lateral border of the basilar part articulates with the posterior border of the petrous part of the temporal bone.

The Condylar Part of the Occipital Bone

• It presents superior and inferior surfaces. The inferior surface of the condylar part presents an occipital condyle. The hypo-glossal or anterior condylar canal opens just above the anterolateral side of the occipital condyle.
• Just behind the condyle is the condylar fossa, which may show the opening of the posterior condylar canal.
• The jugular process is a quadrilateral plate present lateral to the posterior half of the occipital condyle.
• The upper surface of the jugular process is deeply grooved for the sigmoid sinus. The superior surface of the condylar part shows a jugular tubercle.

The Foramen Magnum

For structures passing through the foramen magnum

Foramen Magnum Particular Features

The soft tissue relation

Foramen Magnum Articulations

The following bones articulate with the occipital bone:

• Parietal (at lambdoid suture).
• Mastoid (at occipitomastoid suture).
• Sphenoid (at the basisphenoid suture, which gets ossified at about the age of 25 years).

Foramen Magnum Ossification

The squamous part, above the highest nuchal line, ossifies in the membrane. The rest of the bone ossifies in cartilage.

The part above the highest nuchal line may not unite with the rest of the bone and is then called interparietal bone.

Zygomatic Bone

It is situated on the upper lateral part of the face and forms the prominence of the cheek. Each zygomatic bone has a body and two processes (a frontal and a temporal process)

Zygomatic Bone General Features

The frontal process is directed upwards to articulate with the zygomatic process of the frontal bone.

The temporal process extends backward to articulate with zygomatic process of the temporal bone and forms the zygomatic arch. Anteromedially the body articulates with the maxilla.

General Features Body

• The body has three surfaces and five borders. The surfaces are lateral, temporal arid orbital, while bordes are anteroinferior, anterosuperior (orbital), posteromedial, posterosuperior and postero-inferior.
• The lateral surface is convex and presents zygomaticofacial foramen. This surface forms the prominence of the cheek.
• The orbital surface forms the part of the lateral wall and floor of the orbit. It has the zygomatico-orbital foramen.
• The temporal surface is directed posteromedially. It forms the anterior wall of the temporal fossa. The zygomaticotemporal foramen is present on this surface.

Zygomatic Bone Particular Features

The attachments of muscles on the zygomatic bone.

The following bones articulate with the zygomatic bone:

• Frontal, maxilla, greater wing of the sphenoid, and the zygomatic process of temporal.
• Side Determination and Anatomical Position

Hold the bone in such a way that:

• The frontal process should look upwards.
• The smooth concave orbital margin should face upwards and medially.
• The smooth lateral surface should face laterally.
• The direction of the lateral surface will determine the side of the bone

Zygomatic Bone Ossification

The bone ossifies in the membrane

Maxilla

The right and left maxillae take part in the formation of the whole of the upper jaw and part of the hard palate.

Maxilla General Features

Each maxilla consists of a body and four processes, i.e., an alveolar process, a zygomatic process, a frontal process, and a palatine process.

General Features Body

The body is pyramidal and encloses a large maxillary air sinus. Inferiorly, the body bears an alveolar process for the attachment of teeth.

The body possesses four surfaces: anterolateral, posterior, orbital, and nasal.

Anterolateral Surface

It is directed forward and laterally. Above, the anterior surface is limited by the infra¬ orbital margin.

Medially, this surface presents a nasal notch. Below the infraorbital margin, the infraorbital foramen is present. This surface also presents canine eminence, incisive fossa, and canine fossa.

Posterior Surface

It faces backward and laterally. This surface forms the anterior wall of the infratemporal fossa hence, also known as the infratemporal surface.

Inferiorly, this surface shows the maxillary tuberosity, which articulates with the pyramidal process of the palatine bone. Posterior superior alveolar foramina are seen on the surface.

Orbital Surface

It forms the major part of the floor of the orbit. Posteriorly, it forms the anteromedial border of the infraorbital fissure.

There is the presence of an infraorbital groove near the center of the orbital surface. This groove leads to the infraorbital canal anteriorly, which opens on the anterior surface as infraorbital foramen.

Nasal (Medial) Surface

• This surface takes part in the formation of the lateral wall of the nasal cavity.
• The maxillary air sinus opens on this surface as a large maxillary hiatus
• Posterior to the hiatus there is a groove, which is converted into a greater palatine canal by the perpendicular plate of the palatine bone.
• Anteroinferior to the hiatus is the area of the inferior meatus.
• Superior to the inferior meatus is the nasolacrimal groove.
• There is the presence of a ridge anterior to the nasolacrimal groove. It is called the conchal crest, which articulates with the inferior nasal concha.

Nasal (Medial) Surface Processes

Zygomatic Process This strong process extends laterally from the body to articulate with the body of the zygomatic bone.

Zygomatic Process – Frontal Process

It extends upwards and medially where its tip articulates with the nasal part of the frontal bone. Anteriorly this process articulates with the nasal bone and posteriorly with the lacrimal bone.

The label surface of this process has a ridge called as a lacrimal crest, The medial surface is marked by an ethmoidal cress.

Alveolar Process

It extends downwards and carries the sockets for the teeth of the upper jaw.

Palatine Process

It is a horizontal plate, that projects medially from the nasal surface of the body of the maxilla. Medially it articulates with the palatine process of the opposite maxilla to form the anterior % of the hard palate.

It has superior and inferior surfaces and two free borders, i.e., medial and posterior. Posteriorly, it articulates with the anterior border of the horizontal plate of the palatine bone.

Anatomical Position and Side Determination Mold the bone in such a way that:

• The medial border of its palatine process should be in the median plane.
• The frontal process should point upwards.
• Zygomatic process laterally.

Ossification

It ossifies in the membrane from a single centre which appears in the 6th week of JUL.

Ethmoid

It is a single, irregular midline bone situated between two orbits, in the ethmoidal notch of the frontal bone.

The parts, of the ethmoid can be appreciated by seeing a coronal section of the bone. It consists of a midline perpendicular plate, and two cuboidal bony masses on either side (labyrinth), which are connected to the perpendicular plate by a horizontal cribriform plate.

Perpendicular Plate

At the upper end of the perpendicular plate crista galli is present. The crista galli is seen on the floor of the anterior cranial cavity.

The perpendicular plate takes part in the formation of the median nasal septum.

Labyrinths

The right and left labyrinths are fragile, pneumatic bone.

• It consists of many small air spaces (ethmoidal air sinuses). The ethmoidal air sinuses are arranged in the anterior, middle, and posterior groups.
• The walls of these air spaces are very thin and incomplete. The labyrinth is present between nasal and orbital cavities.
• The medial wall of the labyrinth is a part of the lateral wall of the nasal cavity and is bounded by the medial plate.

From this medial plate, there arises superior and middle conchae. Deep to middle concha there is the presence of a hook-like uncinate process and a rounded elevation, the bulla ethmoidale

The lateral wall of the labyrinth is formed by the orbital plate. The orbital plate forms the part of the medial wall of the orbit.

Cribriform Plate

The cribriform plate is the horizontal plate with numerous perforations.

It connects the labyrinths with the median perpendicular plate. The cribriform plate is seen on the floor of the anterior cranial fossa on either side of the crista galli. It also forms the roof of the nasal cavity.

Articulations

• The perpendicular plate articulates with vomer, septal cartilage, frontal, nasal, and sphenoid bone.
• The cribriform plate articulates with the orbital plate and sphenoid bone.
• Labyrinth articulates with frontal, sphenoid, maxilla, lacrimal, perpendicular plate of palatine, and inferior nasal concha.

Ossification

The ethmoid bone ossifies in a cartilaginous capsule. There appear three centers, i.e., one for the perpendicular plate and one each for the labyrinth. The centers for the labyrinth appear labyrinth. The centers for the labyrinth appear All centers unite to form a single bone by the end of the third year of age.

Palatine Bone

It is situated between the maxilla and pterygoid process. It is L-shaped in appearance and consists of perpendicular and horizontal plates. It also has three processes, pyramidal, orbital, and sphenoidal.

Horizontal Plate

The horizontal plate forms the posterior part plate of palatine and inferior nasal concha anterior, posterior, lateral, and medial. The posterior border is free and projects backward in the midline to form the posterior nasal spine.

Perpendicular Plate

• It has two surfaces, maxillary and nasal, and four borders, i.e., anterior, posterior,
• All centers unite to form a single bone by greater palatine which is converted into the greater palatine canal with the help of the maxilla. This surface also forms the medial wall of the pterygopalatine fossa.
• The nasal is L-shaped in appearance (i.e., ethmoidal crest, which articulates with the middle concha of the ethmoid bone, and conchal crest articulates with the inferior concha).
• The right and left pterygoid processes. The posterior border of the perpendicular plate articulates with the medial pterygoid Body plate.
• The superior border of the perpendicular plate bears an orbital process and a sphenoidal process.
• Between these two processes, there is the presence of a sphenopalatine notch, which is converted into sphenopalatine foramen with the body of the sphenoid.

Pyramidal Process

• The pyramidal process is directed backward and laterally from the junction of horizontal and perpendicular plates.
• This process fits into a pterygoid fissure of pterygoid processes. Its inferior surface presents lesser palatine foramina.

Orbital Process

It is present at the anterior end of the upper border of the perpendicular plate. It forms the posterior part of the floor of the orbit.

Sphenoidal Process

It is situated at the posterior end of the upper border of the perpendicular plate. This process is grooved to complete the palatinovaginal canal.

Sphenoid Bone

It is a single, irregular, pneumatic bone situated posterior to the ethmoid and frontal bone. It forms the middle part of the base of the skull.

Sphenoid Bone General Features

The sphenoid consists of:

• A centrally placed body
• A pair of greater and lesser wings.

Sphenoid Bone Body

• The body of the sphenoid is cuboidal in shape and contains a pair of sphenoidal air sinuses. It has six surfaces (i.e., superior, inferior, anterior, posterior, and right and left lateral surfaces).
• The superior surface of the body bears the hypophyseal fossa. It forms the posterior part of the anterior cranial fossa (jugum sphenoidale, sulcus chiasmaticus, and tuberculum sellae) and the central part of the middle cranial fossa (hypophyseal fossa, dorsum sellae, and posterior clinoid process).
• The inferior swap of the body forms the posterior part of the roof of the nasal cavity and the roof of the nasopharynx. It shows a median ridge called a rostrum, which articulates with the grooved margin of the vomer.
• The anterior surface of the sphenoid articulates with the ethmoid. It presents a median ridge called a sphenoidal crest for articulation with the perpendicular plate of the ethmoid bone. On either side of the crest lies a thin plate of bone called sphenoidal concha. The sphenoidal foramen lies above and medial to the concha.
• The posterior surface is rough and articulates with the basilar part of the occipital bone.
• The upper part of the lateral surface is seen in the floor of the middle cranial fossa and shows a shallow groove the carotid sulcus. The lower part of the lateral surface unites with the greater wing and medial pterygoid plate.

Sphenoid Bone Wings

Sphenoid Bone Greater Wings

• Each greater wing has three surfaces, i.e., cerebral (upper), orbital, and lateral.
• The cerebral surface forms a part of the middle cranial fossa and is related to the temporal lobe of the cerebrum.
• Anteromedially, it has a sharp free margin, which forms the inferolateral boundary of the superior orbital fissure. This surface shows the presence of foramen rotundum, ovale, and spinosum.
• The lateral surface of the greater wing of the sphenoid is divided into the upper temporal surface and lower infratemporal surface.
• The infratemporal surface forms the roof of infratemporal fossa. This surface shows the opening of foramen ovale and spinosum.
• This surface also shows the presence of the spine of the sphenoid, which is present posterolateral to the foramen spinosum. At the junction of the temporal and infratemporal surfaces, there is the presence of an infratemporal crest.
• The orbital surface is quadrilateral in shape and forms part of the lateral wall of the orbit. This surface concerns the superior orbital fissure (above) and inferior orbital fissure.

Sphenoid Bone Lesser Wings

It extends laterally from the anterosuperior part of the body of the sphenoid.

• It is connected to the body by anterior and posterior roots. In between the two roots and the body of the sphenoid, there is the presence of the optic canal.
• The lesser wing consists of two surfaces (superior and inferior) and two borders (anterior and posterior).
• The superior surface forms the posterior-most part of the floor of the anterior cranial fossa. The inferior surface forms the superior border, of the superior orbital fissure.
• The anterior border articulates with the posterior border of the orbital plate, while the posterior border is free.
• The medial end of the posterior border ends in the anterior clinoid process.

Pterygoid Processes

• The pterygoid processes, on either side, extend downwards from the junction of the root of the greater wing and body of the sphenoid.
• Each process consists of lateral and medial pterygoid plates, which are separated posteriorly from each other by pterygoid fossa.
• Anteriorly both the plates are continuous with each other and form the posterior wall of the pterygopalatine fossa.
• Following three foramina open anteriorly in the pterygoid process—foramen rotundum, pterygoid canal, and palatinovaginal canal

Sphenoid Bone Articulations

• Body of sphenoid Ethmoid bone (anteriorly), basilar part of the occipital (posteriorly)
• The lesser living of the Orbital plate of the frontal bone sphenoid anteriorly
• Greater wing of Frontal bone (anterosphenoid medially)
• Zygomatic bone (anterolaterally)
• Parietal bone (superiorly)
• Squamous temporal bone (posterolateral) Petrous temporal (posteriorly) Pterygoid process Maxilla (anteriorly) Perpendicular plate of palatine (Medial pterygoid plate)
• Pyramidal process of palatine (Lower ends of pterygoid plates).

Sphenoid Bone Ossification

The sphenoid gets ossified partly in the membrane and partly in cartilage.

Sphenoid Bone Temporal Bone

The temporal bone is situated on each side of the base and side of the skull.

This bone consists of the following parts:

• Squamous.
• Petrosal.
• Mastoid.
• Tympanic.
• Styloid process.

Sphenoid Bone Squamous Part

• It is a thin plate-like bone. It forms the anterosuperior part of the bone. It has external (temporal) and internal (cerebral) surfaces and a superior and an anteroinferior border.
• The external surface (on the lateral aspect) shows the zygomatic process, roots of the zygomatic process, supramastoid crest, temporal lines, and supra-meatal triangle.
• The external surface (on the inferior aspect) is made up of a small infratemporal suiface, articular tubercle, mandibularfossa and scfuamotympanic fissure.
• The internal or cerebral surface is concave and shows an impression of the gyri of the cerebrum and blood vessels.

Mastoid Part of Sphenoid Bone

• It lies posterior to the squamous part. It shows external and internal surfaces and a posterior border.
• It bears a downward extending conical projection, the mastoid process.
• The outer surface is smooth and may show the opening of the mastoid foramen near its posterior border.
• The inner surface is marked by a vertical groove for the sigmoid sinus.
• The medial surface of the mastoid process shows a deep groove called the mastoid notch and a shallow groove for the occipital artery.

Petrous Part of Sphenoid Bone

• This part of the bone is triangular and present at the base of the skull.
• It has a base, an apex, three borders (superior, anterior, and posterior), and three surfaces (anterior, posterior, and inferior). The bone contains the internal and middle ear cavities

Base of Sphenoid Bone

• The base of the petrous bone is directed backward and laterally and fuses with the squamous and mastoid parts.

Apex of Sphenoid Bone

It is directed forward and medially. It forms the posterior margin of the foramen lacerum.

Borders of Sphenoid Bone

• The superior border demarcates the middle cranial fossa from the posterior cranial fossa. It is grooved by the superior petrosal sinus.
• The medial part of the anterior border articulates with the greater wing of the sphenoid and the lateral part fuses with the squamous part.
• The medial part of the posterior border forms a sulcus for the inferior petrosal sinus.
• The lateral part forms the boundary of the jugular foramen.

Surfaces of Sphenoid Bone

The anterior surface of the petrous bone forms the posterior wall of the middle cranial fossa and shows the following features from medial to the lateral side trigeminal impression, hiatus for greater petrosal nerve, hiatus for lesser petrosal nerve, arcuate imminence, and tegmen tympani.

The posterior surface forms the anterior wall of the posterior cranial fossa and shows the opening of the internal acoustic meatus.

The inferior surface of the petrous bone is rough and presents the lower opening of the carotid canal and depression of the jugular fossa in front of the jugular foramen.

The Tympanic Part of Sphenoid Bone

• It is a curved plate of bone, situated anterior and inferior to the external acoustic meatus. It forms the non-articular posterior wall of the mandibular fossa.
• This plate forms the anterior, inferior, and lower part of the posterior wall of the external acoustic meatus.
• The superior border of the tympanic plate meets the squamous temporal bone at the squamotympanic fissure. The inferior border forms a sheath for the base of the styloid process.
• The rough lateral margin of the tympanic plate gives attachment to the cartilaginous part of the external acoustic meatus.

The Styloid Process of Sphenoid Bone

The styloid process is a conical projection of about 2.5 cm long. It is present on the inferior aspect of the temporal bone.

It is directed downwards forward and medially. The root of the styloid process is ensheathed by the tympanic plate. The stylomastoid foramen is situated between the styloid and mastoid process.

Side Determination and Anatomical Position Hold the bone in such a way that:

• The zygomatic process faces anteriorly.
• External acoustic meatus laterally.
• The mastoid process faces backward and downwards

Articulations of Sphenoid Bone

Squamous part – With greater wing of sphenoid anteriorly With the parietal bone superiorly With the head of the mandible at the temporomandibular joint.

Petrous part – With the greater wing of the sphenoid anteriorly With the occipital bone posteriorly

Mastoid part- With the parietal bone superiorly With the occipital bone posteriorly and medially.

Zygomatic Process- With the temporal process of zygomatic bone.

Bones Of The Upper limb

The Upper limb consists of many regions. The following bones are present in various regions of the upper limb

Pectoral Region

It consists of two bones on each side, i.e., clavicle and scapula. These two bones form the pectoral or shoulder girdle. The lateral end of the clavicle articulates with the scapula at the acromioclavicular joint.

The medial end of the clavicle articulates with the sternum (axial skeleton) through the sternoclavicular joint. Thus the pectoral girdle serves to attach the upper limb to the trunk.

Arm

This region consists of a single bone called as humerus. The upper end of this bone articulates with the scapula at the shoulder joint. The lower end of the humerus articulates with two long bones of the forearm, i.e., the radius and ulna at the elbow joint.

Upper Limb Bones

Forearm

The ulna is medial while the radius is laterally placed in the forearm. At their lower ends, they articulate with carpal bones to form wrist joints.

Hand

The skeleton of the hand consists of many bones ie., carpals, metacarpals, and phalanges. These bones form many joints i.e., intercarpal, sternal facet carpometacarpal, metacarpophalangeal, and interphalangeal joints.

Read and Learn More Human Osteology Notes

Bones form many joints i.e., intercarpal, sternal facet carpometacarpal, metacarpophalangeal, and interphalangeal joints.

The Clavicle or Clavicle Anatomy

Trapezoid The description of the bone in the following paragraph and the reference will help you to learn the “side determination” and “anatomical position” of bone.

costalFacet for cartilage first Subcostal groove Acromian facet The clavicle (collar bone) is a horizontal or inferior surface of a right-placed long bone, which shows two ends (medial and lateral) and a shaft.

Upper Limb Bones

Clavicle Bone

The medial end is thick and rounded Side Determination while the lateral end is broad and flattened. The shaft shows “S” shaped double curvatures, which meet each other at the junction of medial 2/3 and lateral 1/3 of the bone.

The medial 2/3 of the bone is cylindrical and convex forwards, while the lateral 1/3 of the shaft is flattened and concave forwards. The superior surface of the bone is smooth as it is subcutaneous.

On the other hand, the inferior surface is rough near its medial and lateral ends due to the attachment of ligaments. The inferior surface also shows the presence of a shallow groove in its middle third.

 Clavicle Anatomy or Clavicle Side Determination

• Hold the bone horizontally in such a way that its rounded thick end is nearer to the median plane (placed medially) and the flattened end is directed laterally.
• Identify the rough inferior surface and smooth superior surface. Keep the inferior surface facing inferiorly (towards the ground).
• The convexity of the medial 2/3 of the shaft should be directed anteriorly.
• In this position, the lateral end will direct the side of the bone.

Clavicle Bone or Clavicle Anatomical Position

Hold the clavicle horizontally in such a way that its medial end is directed slightly forward and inferiorly as compared to its lateral end (which is directed upward and backward).

Clavicle General Features

For ease of understanding the clavicle is divided into medial 2/3 and lateral 1/3.

Medial 2/3 of Clavicle

Hold the bone in an anatomical position and note the following.

1. It consists of a cylindrical shaft and a thick rounded medial (sternal) end.
2. As the shaft is cylindrical borders are ill-defined (not well marked).
3. There are four surfaces, i.e., superior, inferior, anterior, and posterior. In the absence of well-defined borders, these surfaces are continuous with each other.
4. The superior surface is mostly smooth. It is covered by skin and platysma muscle.
5. The anterior surface of the medial 2/3 of the clavicle is convex anteriorly.
6. The posterior surface is smooth and concave posteriorly.

Clavicle Bone

Now turn the bone upside down to the clavicular joint. see the inferior surface.

1. The inferior surface has a large rough Particular Features impression near its medial end, which gives attachment to a ligament.
2. There is the presence of a shallow groove in the middle third of the inferior surface. This groove is known as the subclavian groove.

The medial end of the clavicle shows a large smooth saddle-shaped articular surface on its medial aspect (sternal surface), which also extends for a short distance on the inferior surface of the bone.

The medial end of the clavicle articulates with the manubrium sterni (at sternoclavicular joint) and also with the first costal cartilage near its inferior surface.

Lateral 1/3 of the Clavicle

As the lateral 1/3 of the clavicle is flat. It shows well-defined anterior and posterior sternohyoid borders and superior and inferior surfaces.

• Hold the bone in the anatomical position and note the following:
• The anterior border is concave forwards and Subclavius shows a small rough area called a deltoid tubercle.
• The posterior border is rough and convex posteriorly.
• The superior surface is mostly smooth except near its anterior and posterior borders, which give attachment to muscles. Now turn the bone upside down to see the inferior surface of lateral1/3.
• The inferior surface near its posterior border shows a tubercle known as conoid tubercle.
• A thick ridge extends forward and laterally from the conoid tubercle. This ridge is known as the trapezoid ride.

The lateral end of the bone bears a small oval facet for articulation with the acromian process of the scapula to form an acromioclavicular joint.

Upper Limb Bones

Particular Features Muscles Attached to Bone

Draw the attachments of muscles on the surface of the bone with the help of colored chalk.

Medial 2/3 of Clavicle

• The superior surface is covered by skin and platysma muscle. The clavicular head of the sternocleidomastoid muscle arises from the medial third of this surface.
• The anterior surface of the medial half of the clavicle gives origin to the clavicular head of pectoralis major.
• The muscle sternohyoid is attached near the medial end of the posterior surface of the clavicle.
• On the inferior surface, the subclavius muscle is attached to the subclavian groove.
• The margins of this groove give attachment to clavipectoral fascia.

Lateral 1/3 of the Clavicle

• The anterior border gives origin to the deltoid muscle.
• The posterior border gives attachment to the trapezius muscle.
• Costoclavicular ligament
• Ligaments Attached to Bone
• The attachments of the articular capsule at its medial and lateral ends are shown in.
• The costoclavicular ligament is attached to the inferior rough surface near its medial end.

• The interclavicular ligament and the articular disc of the sternoclavicular joint are attached to the medial surface of the medial end.
• Conoid and trapezoid parts of the coracoclavicular ligament are attached on the conoid tubercle and trapezoid ridge respectively on the inferior surface of lateral 1/3.

Upper Limb Bones

Nerves and Blood Vessels Related To Bone

• Three supra-clavicular nerves (medial, intermediate, and lateral) are related to its anterosuperior surface.

• There lasted posterior to the surface trunks of medial brachial 2/3 of the plexus, shaft in the third part of subclavian vessels, and internal jugular vein.

Clavicle Fracture

Peculiarities of the Clavicle

• Though it is a long bone but is placed horizontally.
• Though long bone but ossifies mostly from membrane.
• It is devoid of a medullary cavity.
• The first bone to start ossifying in the body.

Clavicle Clinical Application

The main function of the clavicle is to transmit the forces from the upper limb to the axial skeleton through the sternoclavicular joint.

The forces are transmitted from the humerus to the scapula and then from the scapula to the clavicle through the coracoclavicular ligament. If the force, during a fall on the outstretched hand, is greater than the strength of the clavicle, a fracture will result at the junction between two curvatures of bone (medial 2/3 and lateral 1/3).

After the fracture, the shoulder drops, and the lateral fragment of the clavicle is displaced downward due to the weight of the upper limb (gravity).

Clavicle Fracture

The medial fragment of bone is pulled upward due to the action of the clavicular head of the sternocleidomastoid muscle.

The lateral fragment of the bone may also be pulled medially by the action of the pectoralis major.

Thus two fragments may override each other. To approximate the two fractured ends of the bone, a bandage in the shape of a figure of eight is tied.

The clavicle acts as a strut to keep the shoulder laterally. This helps the upper limb to swing away from the trunk.

In a congenital malformation known as cleidocranial dysostosis, the clavicle is either absent or imperfectly developed.

In this condition shoulder joint is not always placed laterally and can be brought in front of the chest.

• The concave posterior surface of medial 2/3 of the bone protects the nerves and vessels (trunks of brachial plexus and subclavian vessels), which go from the root of the neck to the axilla.

Clavicle Fracture

Clavicle Ossification

The clavicle is the first long lone to ossify in the embryo. It is organized by two primary centers and one secondary center. Most of the shaft ossifies by membranous ossification.

The Scapula or Scapula Bone

The description of the scapula is in the following two paragraphs and a reference will help you learn to determine its side and to keep it in the anatomical position. The scapula is also known as the “shoulder blade”.

It is the posterior bone of the shoulder girdle. It lies on the posterolateral aspect of the thorax extending between the 2nd and 7th rib.

The body- of the scapula is thin, flat, and triangular.

Upper Limb Bones

As the body is triangular it has three borders (medial, lateral, and superior) and three angles (superior, lateral, and inferior).

The inferior angle is directed downwards and lies at the level of the 7th rib. Just opposite the inferior angle is a superior border that extends between superior and lateral angles.

Scapula Bone

At the lateral angle, there is the presence of a shallow smooth articular fossa called a glenoid cavity, which articulates with the head of the humerus to form a shoulder joint.

The medial border runs between superior and inferior angles and is quite thin. The lateral border is thick and runs between lateral and inferior angles.

The scapula shows two surfaces, i.e., costal and dorsal. The costal (anterior) surface is smooth and forms a shallow fossa called as subscapular fossa.

On the other hand dorsal (posterior) surface is convex posteriorly and is divided into supraspinous and infraspinous fossae by the presence of a bony process called as spine of the scapula.

Scapula Bone

It is a thick projecting ridge of bone, which is continuous laterally as the flat expanded acromion process. A beak-like bony process (coracoid process) arises from the upper part of the glenoid cavity.

Scapula Side Determination

Scapula Hold the bone in such a way that:

• The inferior angle is directed downwards and the superior border is directed upwards.
• The costal or anterior surface should face anteriorly and the dorsal (posterior) surface, bearing the spinous process, should face posteriorly.
• The glenoid cavity should face laterally.

• In this position, the direction of a glenoid cavity will determine the side of the bone.

Scapula Anatomical Position

• Hold the bone in such a way that the coastal surface should face antero-medially.
• The glenoid cavity should face anterolaterally and slightly upwards.

Scapula General Features

We shall study the general features of the scapula under four different headings, i.e., surfaces, borders, angles, and processes.

Surfaces

Costal (anterior) surface: The costal surface is slightly concave and forms a large subscapular fossa. There is the presence of a bar of thickened bone near the lateral border extending. between the head of scapula (lateral angle) and the inferior angle.

Dorsal (posterior) surface: The spine of the scapula divides the dorsal surface into a smaller upper supraspinous fossa and a larger infraspinous fossa. Both these fossae are continuous with each other through spinoglenoid notch.

Borders

Medial border: The medial border of the scapula is thin and lies about 5 cm lateral to the spinous processes of the thoracic vertebrae.

Lateral border: This border extends from the lowest part of the glenoid cavity to the inferior angle.

It is a sharp ridge. Close to the lateral border, on the costal surface, there is the presence of a thickened longitudinal bar of the bone. It should not be confused with the lateral border.

Superior border: It extends between the superior angle and the root of the coracoid process. This border presents a suprascapular notch close to the root of the coracoid process.

Angles

The superior and inferior angles of the scapula are present at the upper and lower ends of the medial border respectively.

The lateral angle of the scapula is the thickest part of the bone where the glenoid cavity is present. This broadened part of the bone is sometimes called as head of the scapula. A constriction between the head and body is called as neck of the scapula.

The glenoid cavity is a shallow, concave, oval fossa. There is a presence of rough areas just above and below the glenoid cavity. These are called supraglenoid and infraglenoid tubercles respectively.

Scapula Processes

The spine of the scapula is a triangular bony process present on the dorsal aspect of the body. Its anterior border is attached to the dorsal surface of the body while its posterior border is free.

This thick posterior border of the spine is also known as the crest of the spine. The lateral border of the spine forms the boundary of the spinoglenoid notch.

The acromion process is a forward projection from the lateral end of the spine. It is a flat, expanded, subcutaneous process, which overhangs the glenoid cavity.

It has medial and lateral borders and superior and inferior surfaces. It articulates with the lateral end of the clavicle to form an acromioclavicular joint. The coracoid process is so named because it resembles the beak of a crow.

It is present superior to the glenoid cavity and is shaped like a bent finger. In the anatomical position, it projects anterolaterally.

Scapula Particular Features

Muscles Attached to Bone

Draw the attachments of muscles on the surface of the bone with the help of colored chalk as shown in

• Almost the whole of the costal (anterior) surface (except a small part near the neck) gives origin to the subscapularis muscle.
• The medial border on the costal surface gives attachment to the serratus anterior.

• The inferior belly of the omohyoid is attached to the superior border near the suprascapular notch.
• On the dorsal surface, the supraspinous fossa gives origin to the supraspinatus muscle and infraspinous fossa to the infraspinatus respectively.
• The teres major and teres minor arise from the dorsal surface close to the lateral border.
• Attachments of levator scapulae, rhomboideus minor, and rhomboideus major on the dorsal surface of the medial border.
• The supraglenoid tubercle gives origin to the long head of biceps brachii.
• The long head of the triceps arises from the infraglenoid tubercle.
• The coracobrachialis and short head of biceps arise from the tip of coracoid process.
• Pectoralis minor is inserted on the superior aspect of the coracoid process.
• The deltoid muscle arises from the lower border of the crest of the spine and the lateral border of the acromion process.
• The medial border of the acromion and upper border of the crest of the spine gives insertion to the trapezium.

Ligaments Attached to Bone

• The attachments of the capsule of the shoulder joint and acromioclavicular joints.
• The suprascapular ligament is attached to the superior border above the suprascapular notch
• Three ligaments are attached to the coracoid process, i.e., coracohumeral, coracoacromial, and coracoclavicular.
• One end of the coracoacromial ligament is attached to the lateral border of the coracoid process and the other end is to the tip of the acromian process. The coracohumeral is attached to the root of the coracoid process.
• The conoid part of the coracoclavicular ligament is attached near the root, while the trapezoid part is on the superior aspect of the coracoid process.

Nerves and Blood Vessels Related to the Bone

The suprascapular vessels lie above the suprascapular ligament, while the suprascapular nerve passes deep to it These vessels and nerves then lie in These vessels and nerve then lie in spinoglenoid notch.

• The circumflex scapular branch of the subscapular artery comes in contact with the lateral border on its dorsal aspect between two heads of teres minor.
• The dorsal scapular nerve and vessels lie close to the medial border.

Scapula Ossification

The scapula ossifies by one primary and 7 secondary centers (2 for the coracoid process, 2 for acromion, 1 each for the glenoid cavity, inferior angle, and medial border).

The lower center of the coracoid process fuses with the body by the 16th year while other centers by the end of the 20th year.

Humerus

The humerus is the longest bone of the upper limb. It has two ends and a shaft. The proximal (upper) end shows a large, smooth, rounded head that articulates with the glenoid cavity of the scapula to form the shoulder joint. The head is directed medially.

There is the presence of a deep vertical groove {inter-tubercular sulcus or bicipital groove) on the anterior aspect of the upper end.

The middle part of the shaft is almost cylindrical. The lower end is expanded from side to side and flattened from before backward. It has two articular structures, i.e., a rounded capitulum and the pulley-shaped trochlea.

On the posterior aspect of the lower end, there is a large olecranon fossa just above the trochlea. The medial and lateral epicondyles are bony non-articular projections at the lower end.

Humerus Side Determination

• You should keep the bone vertical in such a way that the head faces medially.

• The intertubercular sulcus on the anterior aspect of the upper end should face anteriorly.
• The olecranon fossa, at the lower end, should face posteriorly

Humerus Anatomical Position

Hold the bone vertically in such a way that the head faces medially and slightly upwards and backward.

Humerus General Features

We shall study the general features of bone under three headings, i.e., upper end, shaft, and lower end

Humerus Upper end

The upper end consists of the head, neck, greater and lesser tubercles, and an intertubercular sulcus (bicipital groove).

• The head has a convex, rounded, and smooth articular surface.
• The junction of the articular head with the rest of the upper end is called as anatomical neck.
• The junction of the upper expanded end with the shaft is called a surgical neck.
• The lesser tubercle is present on the anterior aspect of the upper end while greater tubercle is present on its anterolateral aspect.
• There is the presence of an intertubercular sulcus between these two tubercles.
• Both the tubercles on their upper surface show the presence of smooth areas for the attachment of muscles.

Humerus Shaft

The shaft is almost cylindrical in the upper half and triangular in the lower half. It presents three borders and three surfaces.

Borders

• Trace the lateral lip of the bicipital groove downward. You will see that it becomes continuous with the anterior border of the shaft.
• The medial border of the bicipital groove is continuous downwards as the medial border.
• If this border is further traced downwards it becomes continuous as medial supracondylar ridge.

• The lateral border of the shaft is well-defined only in the lower part of the shaft where it becomes continuous with the lateral supracondylar ridge.

Humerus Surfaces

• The anteromedial surface is between the anterior and medial border.
• The anterolateral surface is between anterior and lateral borders. Just above the middle of the bone, this surface shows a V-shaped rough area called deltoid tuberosity.
• The posterior surface is situated between lateral and medial borders. In its middle 1/3, it shows the presence of a shallow groove (radial groove) running downwards and laterally.

Humerus Lower End

• The lower end shows the presence of a rounded articular area known as the capitulum. It is placed laterally and articulates with the upper end of the radius.
• The pulley-like trochlea is placed medially and articulates with the trochlear notch of the ulna.
• There is a presence of shallow fossa above the capitulum (known as radial fossa) and coronoid fossa just above the trochlea. When the forearm is flexed, the coronoid fossa and radial fossa receive the coronoid process and head of radius respectively.
• The olecranon fossa is quite large and situated on the posterior surface of the lower end just above the trochlea. It receives the olecranon of the ulna when the forearm is extended.
• If you will trace the medial and lateral supracondylar ridges downwards, you will reach the bony projections on either side of the lower end.
• These rough projections are known as epicondyles. The medial epicondyle is the prominent subcutaneous projection, which you should palpate (feel) in your limb.

Humerus Particular Features

Muscles Attached to Bone

Upper End

• The three impressions on the surface of the greater tubercle give insertion to supraspinatus, infraspinatus, and teres minor.
• The subscapularis muscle is inserted on the lesser tubercle.
• The tendon of the long head of the biceps passes through the bicipital groove.

Shaft

Shaft Anterior Aspect

• On the anterior aspect of the shaft, the medial lip of the bicipital groove gives attachment to the teres major while the lateral lip to the pectoralis major.
• The floor of the bicipital groove gives insertion to the latissimus dorsi.
• On the V-shaped deltoid tuberosity deltoids are attached.
• The coracobrachialis is attached to the middle of the medial border.
• The brachialis muscle arises from the front aspect of the lower half of the shaft.
• The pronator teres take origin from the medial supracondylar ridge.
• The lateral supracondylar ridge gives origin to the brachioradialis and extensor carpi radialis longus.

Shaft Posterior Aspect

• The lateral head of the triceps arises above the radial groove.
• Below the radial groove, the posterior surface gives origin to the medial head of the triceps.

Shaft Lower End

• The front of the medial epicondyle gives origin to the superficial flexor muscles of the forearm. This origin is known as “common flexor origin”.
• The anterior aspect of the lateral epicondyle gives origin to extensors of the forearm hence known as “common extensor origin”.
• The anconeus originates from the posterior surface of the lateral epicondyle.

Ligaments Attached to Bone

• The attachments of the articular capsule for shoulder joint and elbow joints.
• The ulnar collateral ligament of the elbow joint is attached to the medial epicondyle.
• The radial collateral ligament is attached to the lateral epicondyle.

Nerves and Vessels Related to the Bone

The surgical neck of the humerus is related to the anterior and posterior circumflex humeral vessels and the axillary nerve.

• The radial nerve and profunda/brachial vessels are related to the radial groove.
• The ulnar nerve lies just posterior to the medial epicondyle.

Shaft Clinical Importance

• The common sites of fracture are the surgical neck, middle of the shaft, and supracondylar region.
• The fracture of the surgical neck of the humerus is common in old people. The axillary nerve, which is in direct contact with the neck, may get injured.
• The supracondylar fractures are common in young individuals. The median nerve and brachial artery may get injured as they are related to the lower end.
• The fracture of the middle of the shaft may be due to a direct blow to the arm. Here the radial nerve in the radial groove may get injured.
• The avulsion fractures of the greater tubercle of the humerus are also common (in this fracture the greater tubercle is pulled away from the rest of the upper end). This may result in to fall on the hand while the arm is abducted.
• The fracture of the medial epicondyle is usually associated with the injury of ulnar nerve, as it lies just posterior to the epicondyle.
• As the upper end of the humerus is the growing end, the bone keeps on growing in a young individual even after the amputation of an arm.
• Hence, at the time of amputation of the arm care should be taken that sufficient soft tissue should be left distal to the site of amputation so the bony stump will not penetrate soft tissues.

Shaft Ossification

The upper end ossifies by 3 and the lower end by 4 secondary centers Upper end is the growing end as the secondary center appears first and fuses last (at 20 years).

Radius

• The radius is situated on the lateral side (thumb side) of the forearm. Like any other long bone, it also consists of the upper end, shaft, and lower end.
• The upper (proximal) end of the radius is narrow while its lower end is wide. The upper end presents a disc-shaped head, a neck, and medially directed radial tuberosity.
• The shaft of the radius has a laterally directed convexity. The medial border is sharp and called an interosseous border. The lower end is wide and shows anterior, posterior, medial, and lateral surfaces.
• The posterior surface of the lower end is rough and presents a dorsal tubercle. A projection (styloid process) is present on the lateral aspect of the lower end.

Radius Side Determination

• Keep the bone vertically in such a way that the narrow disc-shaped upper end is directed upward (proximally).
• At the expanded lower end, the dorsal tubercle should face backward and styloid process directed laterally and downwards.
• In this position, a sharp border of the shaft (interosseous border) should be directed medially.

Radius Anatomical Position

Hold the bone vertically in such a way that the head is directed upwards, with radial tuberosity and sharp border medially, and dorsal tubercle posteriorly.

General Features Upper End

The upper end consists of the head, neck, and radial tuberosity.

• The disc-shaped head shows an upper surface, which is slightly concave to articulate with the capitulum of the humerus.
• The circumference of the head articulates medially with the radial notch of the ulna to form the superior radioulnar joint. The rest of the circumference of the head is surrounded by an annular ligament.
• The constriction just below the head is known as the neck.
• There is a prominent elevation just below the medial part of the neck. This is known as radial tuberosity.

Shaft

• The shaft shows 3 borders and three surfaces.
• Trace the anterior border from the anterior aspect of radial tuberosity to the styloid process.
• Trace the posterior border from the posterior Upper-End aspect of the radial tuberosity to the posterior aspect of the lower end Trace the sharp medial (interosseous) border from the lower aspect of radial tuberosity to the posterior margin of the ulnar notch.
• The anterior surface lies between anterior and medial borders while the posterior surface lies between posterior and medial borders.
• The lateral surface is present between anterior and posterior borders. This surface is convex laterally and shows a rough area near the middle part of the shaft.

Lower End

• The lower end is the expanded end and shows anterior, posterior, lateral, and medial surfaces.
• It also shows an inferior surface, which is smooth (articular) and articulates with the scaphoid laterally and lunate bone medially to form the wrist joint
• The lateral surface when traced downwards, projects as a styloid process.
• The medial surface shows an ulnar notch. It articulates with the head of the ulna to form an inferior radioulnar joint.

Radius Particular Features

Muscles Attached to the Radius

Upper End

The biceps brachii is inserted on the rough posterior part of the radial tuberosity. The anterior smooth part of the radial tuberosity is in relation with the bursa.

Shaft and Lower End

• The upper part of the anterior border gives origin to the radial head of flexor digitorum superficialis.
• The upper of the anterior surface gives origin to the flexor pollicis longus.
• The pronator quadratus is inserted into the lowermost part of the anterior surface. The attachment also extends on the medial surface of the lower end. posterior surfaces give insertion to the supinator.
• The rough area on the middle of the lateral surface gives insertion to pronator teres.
• The muscle brachioradialis is inserted into the lowest part of the lateral surface just above the styloid process.
• The abductor pollicis longus and extensor pollicis brevis arise from the posterior surface of the shaft.

Ligaments Attached to the Bone

• Note the attachment of the articular capsule of the wrist joint on the lower end of the radius.
• The interosseous membrane is attached to the lower 3A of the medial border.
• The articular disc of the inferior radioulnar joint is attached to the lower border of the ulnar notch.
• The anterior border near the lower end gives attachment to the extensor retinaculum.
• The radial collateral ligament of the wrist joint is attached to the tip of the styloid process.

Tendons and Arteries with the Bone

• The relationship of tendons on the dorsal aspect of the lower end
• The radial artery is related to the anterior surface of the lower end. Here the pulsations of the artery can be easily felt by applying pressure against the radial bone.

Radius Clinical Importance

Though the fracture of the radius may occur at its upper end and shaft the fracture of the distal end of the radius is most common, especially in old women.

A fracture of the lower end of the radius is called a Colies’s fracture. The fracture usually results from a fall on an outstretched hand.

The distal fragment overrides and is displaced dorsally. This results in a shortening of radius.

As a result the styloid process of both the bones (radius and ulna) now lies almost at the same level. The clinical deformity is often referred to as “dinner fork deformity.

Radius Ossification

Radius ossifies by one primary and two secondary centers, i.e., one for each end. The lower end is the growing end.

Ulna

• The ulna is the medial bone of the forearm. It is longer than the radius. The ulna has an upper end, a lower end, and a shaft. The upper end of the ulna is expanded, and irregular and presents a deep notch, which faces anteriorly.
• This notch is called a trochlear notch and it articulates with the trochlea of the humerus at the elbow joint. While its lower end is small and has a tiny styloid process.
• You should remember that the lower end of the ulna is called as head. The shaft has a sharp lateral margin.
• This margin gives attachment to the broad, flat, fibrous connective tissue called interosseous membrane. The ulna is connected with the radius by an interosseous membrane.

Ulna Side Determination

• Hold the bone vertically in such a way that its expanded hook-like end is directed upwards and the small rounded lower end is directed downwards.
• The concavity of the trochlear notch (at the upper end) should face anteriorly.
• The sharp border of the shaft should be directed laterally.

Ulna Anatomical Position

Hold the bone vertically in such a way that the trochlear notch faces anteriorly, the sharp border of the shaft laterally, and the styloid process at the lower end is present posteriorly.

Ulna General Features

Ulna Upper End

The upper end of the ulna presents the olecranon process, coronoid processes, and two articular surfaces, i.e., trochlear and radial notches.

Olecranon Process

• The olecranon process is the uppermost part of the ulna. It has superior, anterior, posterior, medial, and lateral surfaces.

• The anterior surface of the olecranon process forms the upper part of the trochlear notch.
• The posterior surface of this process is triangular and smooth because it lies just beneath the skin.

Coronoid Process

• The coronoid process projects anteriorly from the shaft just below the olecranon.
• It has four surfaces, i.e., superior, anterior, medial, and lateral.
• The superior (upper) surface is almost horizontal and forms the lower part of the trochlear notch.
• The anterior surface is triangular and is rough in its lower part. The rough area is known as the tuberosity of the ulna.

Radial Notch

The lateral surface of the coronoid process has a concave articular area. This is known as a radial notch. It articulates with the head of radius forming the superior radioulnar joint.

Trochlear Notch

• It articulates with the trochlea of the humerus. It is formed by the anterior surface of the olecranon and the upper surface of the coronoid process. There may be a non-articular area(groove) between the two parts.

Lower End

• The lower end (head) is small and rounded.
• Anteriorly and laterally it articulates with the ulnar notch of the radius to form an inferior radioulnar joint.
• The inferior surface is separated from the cavity of the wrist joint by an articular disc.
• The styloid process projects downwards from the posteromedial aspect of the lower end.

Shaft

• The cross-section of the shaft is almost triangular.
• It presents anterior, lateral, and posterior borders and anterior, medial, and posterior surfaces.
• The lateral or interosseous border is sharp. When traced upwards, it becomes continuous with a rough ridge present just posterior to the radial notch. This rough ridge is known as the supinator crest.
• The anterior and posterior borders are rounded. The anterior border begins at the lower end of the tuberosity of the ulna and ends on the anterior aspect of the styloid process.
• The anterior surface lies between the anterior and interosseous border and shows the presence of an oblique ridge in its lower part.
• The posterior surface lies between inter osseous and posterior border. The posterior surface is subdivided into medial and lateral parts by a vertical ridge.

Ulna Particular Features

Muscles Attached to Bone

Upper End

• The triceps is inserted on the posterior part of the upper surface of the olecranon process.
• Brachialis is attached to the anterior surface of the coronoid process and the tuberosity of the ulna.
• The supinator arises from the supinator crest and a triangular area just below the radial notch.

• The medial border of the coronoid process gives origin to the ulnar head of flexor digitorum superficialis above and pronator teres below.
• The anconeus is inserted into the lateral aspect of the olecranon and the upper part of the posterior surface of the shaft.
• The ulnar head of the pronator teres arises from the medial margin of the coronoid process.
• The ulnar head of the flexor carpi ulnaris arises from the medial side of the olecranon process and from the upper two-thirds of the posterior border through aponeurosis.
• From the same aponeurosis, ulnar head of extensor carpi ulnaris also arise.

Shaft

• Flexor digitorum profundus takes origin from the anterior and medial surface of the shaft On the anterior surface the oblique ridge gives origin to the pronator quadratus
• Three muscles are attached on the posterior surface (between the interosseous border and a vertical ridge) from above downwards i.e., abductor pollicis longus, extensor pollicis long, and extent or indices.

Ligaments Attached to Bone

• The capsular ligament of the elbow joint is attached to the margins of the coronoid and olecranon process.

• The capsular ligament of the inferior radioulnar joint is attached close to the articular area.
• The apex of the triangular articular disc is attached to the lateral aspect of the styloid process.
• The interosseous membrane is attached to the sharp interosseous border.
• The annular ligament of a superior radioulnar joint is attached to the anterior and posterior border of the radial notch.
• The oblique cord is attached to the lateral aspect of the ulnar tuberosity.
• The ulnar collateral ligament of the wrist joint is attached to the tip of the styloid process.

Ulna Clinical Importance

• Though the fractures of both the radius and ulna may result due to severe injury isolated fractures of the radius and ulna may also occur.
• The most common fracture of the ulna along with the radius is through the middle of the shaft or at its lower end. Sometimes a fracture of the olecranon can occur due to a fall on the elbow.

Ulna Ossification

Ulna ossifies by 3 centers, i.e., one primary and two secondary, i.e., one each for upper and lower end. The lower end is the growing end.

Bones Of The Hand

The bones of the hand consist of carpals, metacarpals, and phalanges.

Carpal Bones

The skeleton of the wrist consists of eight small bones, which are arranged in two transverse rows of four bones each. These bones are called carpal banks. They are named as per their shapes.

The proximal row, from lateral to medial side, consists of:

• Lunate (It is moon-shaped).
• Triquetrum (It has three corners and is pyramidal). Pisiform (It is pea shaped small bone that lies on the anterior surface of the triquetrum).
• The carpal bones in the distal row, from lateral to medial, are:
• Trapezium (table-shaped, four-sided).
• Trapezoid (wedge-shaped).
• Capitate (It is cap-shaped and has a rounded head).
• Hamate (It has a hook-shaped process).

Joints Formed by the Carpal Bones

• The wrist joint is formed between the proximal surfaces of three carpal bones of the proximal row and the lower end of the radius.
• The scaphoid and lunate of the proximal row articulate with the inferior articular surface of the radius, while the triquetrum is related to the articular disc and thus separated from the head of the ulna.
• Carpal bones are joined to one another by interosseous ligaments and intercarpal joints.
• The distal articular surfaces of the carpal bones of the distal row articulate with the metacarpals to form carpometacarpal joints.

Bones of the Hand Clinical importance

• The common injury of the wrist consists of fracture of the scaphoid or lunate.
• The fracture of the scaphoid is the most common. It results in a fall on an outstretched hand. In this condition, the line of fracture passes almost from the middle of the bone dividing the bone into proximal and distal fragments. The patient complains of pain in the scaphoid fossa (lateral side of the wrist.
• As the nutrient arteries scaphoid enter the distal end of the bone, the proximal segment is devoid of the blood supply after fracture. This may result in avascular necrosis (death due to inadequate blood supply) of the proximal fragment of the scaphoid.
• Thus scaphoid fracture heals poorly, i.e., may take several months to heal.
• The fracture of hamate also heals poorly due to the traction produced by the attached muscles.
• As the ulnar nerve lies close to the hook of hamate, it may also get injured due to the fracture of the hamate.

Metacarpals

Metacarpals are miniature long bones, which form the skeleton of the palm. They are five in number and are numbered from the lateral to the medial side. The metacarpal of the thumb is known as the first metacarpal while that of the little finger is known as the fifth (V) metacarpal.

Each metacarpal bone consists of a proximal base, an intermediate shaft, and a distal head.

• The proximal ends or bases of the metacarpal are irregularly expanded and articulate with the carpal bones. The distal ends (heads) are rounded and articulate with the proximal phalanges.
• The shaft of each metacarpal is curved with the concavity looking forward. It has three surfaces, i.e., medial, lateral, and posterior.
• The first metacarpal is easily distinguished from the rest because it is the thickest and shortest of all the metacarpals. The articular surface at its base is concavoconvex which articulates with trapezium.
• The third metacarpal can also be differentiated from the rest because it has a styloid process on the lateral side of its base.

Joints Formed by the Metacarpals

• The distal articular surfaces of the carpal bones of the distal row articulate with the metacarpals to form carpometacarpal joints.
• The trapezium articulates with the first metacarpal, the trapezoid with the second, the capitate with the third, and the hamate with the fourth and fifth metacarpals.
• The distal articular surfaces of metacarpals articulate with the proximal articular surfaces of proximal phalanges to form carpometacarpal joints.

Phalanges

• Phalanges are the bones of digits. Each digit has three phalanges (i.e., proximal, middle Flexor carpi, and distal) except the first (for thumb), which has only two phalanges.
• Each phalanx has a proximal base, a body, and a distal head. The proximal phalanges are the longest and most articulate with the head of metacarpals at their bases to form metacarpophalangeal joints.
• The middle phalanges are intermediate in size and articulate at their bases with the heads of proximal phalanges to form proximal interphalangeal joints.
• The distal phalanges are smallest, flattened, and expanded at their distal ends (non-articular) to form the nail beds.

Particular Features of the Bones of Hand

• Insertion of forearm muscles on the palmar surface of the hand.
• The flexor carpi ulnaris is attached on the pisiform bone. From this bone abductor digiti minimi also takes origin.

• Flexor carpi radialis is inserted on the base of the 2nd and 3rd metacarpals on their palmar surface.
• The flexor digitorum profundus is inserted on the bases of distal phalanges, while flexor digitorum superficialis is inserted on both the sides of middle phalanges of all the fingers except that of the thumb.
• The flexor pollicis longus is inserted on the base of the distal phalanx of the thumb, on its palmar surface.

Insertion of forearm muscles on the dorsal aspect of the hand and dorsal interossei.

• The extensor carpi ulnaris is attached to the base of the fifth metacarpal; the abductor pollicis longus to the base of the first; the extensor carpi radialis longus to the base of the second; extensor carpi radialis brevis to the bases of 2nd and 3rd metacarpal.

Attachments of Ligaments

• The attachment of carpal bones with each other (due to their shape) presents a concavity forward.
• The attachment of the flexor retinaculum medially to the hook of the hamate and pisiform bone and laterally to the tubercles of the scaphoid and trapezium
  form an osteofascial carpal tunnel.
• Through this tunnel passes the tendons, vessels, and nerves from the forearm to the hand.
• Pisiform bone gives attachment to two ligaments, i.e., first extending from pisiform to the base of the fifth metacarpal (pisometacarpal) and second from pisiform to the hook of the hamate (pisohamate).
• The medial end of the extensor retinaculum is attached to the triquetral and pisiform bones.
• The lateral margins of each phalanx give attachment to the fibrous flexor sheath.

Bones Of The Head And Neck Regions

• The bones of the head and neck regions consist of the skull, cervical vertebrae, and hyoid bone.
• The skull forms the skeleton of the head region. the skull contains a large cavity for the lodgment of the brain (called a cranial cavity) and two small cavities for the lodgment of the eyes (called orbits).
• On the anterior aspect of the skull, there are two openings, i.e., the opening of nasal cavity and the opening of the oral cavity (mouth).
• Below the skull, the skeleton of the neck is formed by the seven cervical vertebrae.
• The hyoid bone is a small bone, present in the upper part of the neck in front of the 3rd cervical vertebra.

Anterior Nasal Aperture

Skull

The skull (the skeleton of the head) is formed by 22 bones. These bones are firmly joined to one another and are immobile except for the bone of the lower jaw (mandible), which moves at the temporomandibular joint. The skull is divided into two parts, i.e., cranium and facial skeleton.

Cranium

• It is also known as the neuro-cranium, brain box, or calvaria. The cranium is the upper and posterior part of the skull.
• Cranium means skull minus the mandible.
• It consists of 8 bones. Out of these 8 bones, 4 are unpaired (frontal, occipital, sphenoid mid ethmoid) and 2 are paired (parietal and temporal).
• The joints between these bones are immobile and are known as sutures.
• The cranium has a dome-like roof (called a vault or skull cap) and a floor or cranial base (called basi-cranium.

Anterior Nasal Aperture

Facial Skeleton (Viscerocranium)

• The facial skeleton forms the anterior part of the skull. It contains orbital and nasal cavities and includes upper and lower jaws (maxillae and mandible).
• In addition to the frontal bone, the facial skeleton consists of 14 bones. Out of these 6 are paired (lacrimal, nasal, maxillae, zygomatic, palatine, and inferior nasal conchae). While the mandible and vomer are single bones.

Read and Learn More Human Osteology Notes

Anatomical Position of the Skull

To obtain the anatomical position of the skull, it is kept in the “Frankfurt horizontal plane”.

• Hold the skull in such a way that the inferior border of the orbit and the superior border of the external acoustic meatus of the right and left sides lie in the same horizontal plane.
• Students are suggested to identify various bones of a dry skull with the help. Once they can identify various bones in the skull then only they should proceed to study the details of the skull as seen from various aspects.

Anterior Nasal Aperture

A dry skull may be viewed from:

• Above (norma verticalis,.
• Behind (norma occipitalis,
• Front (norma frontalis). The walls of the orbital cavity can also be examined from this view.
• And from the side (norma lateralis,.
• Below (norma basalis externa,
• The roof of the calvaria (skull cap) may be removed by a transverse cut to examine the inside of the floor of the cranium.
• The interior of the base of the skull (norma basalis interna) is divided into three cranial fossae, i.e., anterior, middle, and posterior. The inner aspect of the skull cap.
• The section of the skull in the para-median plane will help us to study the nasal cavity.

Superior Aspect Of The Skull (Norma Verticals)

When the skull is viewed from above it appears oval. It is relatively wider nearer its occipital pole (posteriorly). The bones forming the skullcap (roof of the brain box) are visible from this aspect.

Anterior Nasal Aperture

Bones Forming the Norma Verticalis

• Frontal bone
• It is a single bone that forms the anterior part of the norma verticalis.
• Parietal bones
• These are paired bones and lie posterior to the frontal bone on each side of the midline.

• Occipital bone—It is a single bone and lies posterior to the parietal bones.

Sutures (Joints) Present in the Normal Verticalis

The following three sutures and their meeting points are seen in this norma:

• Coronal suture—It lies between the frontal and right and left parietal bones.
• Sagittal suture—It is present in the midline between the right and left parietal bones.

Norma Basalis Interna

Lambdoid suture

• It lies between the occipital and two parietal bones.
• Bregma—It is a landmark point, where coronal and sagittal sutures meet each other. It is present in the midline.

Lambda

• It is present at the junction of the sagittal and lambdoid sutures.

Features of Norma Verticalis

• The parietal foramen is present near the sagittal suture about 3.5 cm anterior to the lambda. It transmits a small emissary vein, which connects the superior sagittal sinus with the veins of the scalp.
• Parietal eminence is the area of the maxi¬ mum convexity on the parietal bone. It is present on the posterolateral aspect of the parietal bone.
• Superior and inferior temporal lines are seen on the lateral side of the frontal and parietal bones. The superior temporal line gives attachment to the epicranial aponeurosis and temporal fascia. The inferior temporal line gives attachment to the temporalis muscle.
• The vertex is the highest point of the skull and is situated near the midpoint of the sagittal suture.

Applied Importance

Metopic Suture

The right and left halves of the frontal bone are ossified from separate centers. There exists a frontal suture between two frontal bones before the age of 6 years. In some adult skulls, this suture may persist in full or in part and is known; as a metopic suture.

Sutural Bones

Isolated small bony ossicles (bones) are sometimes observed along the lambdoid and sagittal sutures. These are called sutural bones. They are formed due to; ossification from separate centers

Norma Basalis Interna

Fontanelle

In the skull of a newborn there are membranous I gaps at the site of bregma and lambda. These are called anterior and posterior fontanelles respectively.

The anterior fontanelle closes (the membranous gap of the anterior fontanelle is replaced by bone) by 18 months of age, while the posterior closes by 2 to 3 months of age.

Following are the functions of fontanelle: Fontanelle allows molding of the skull during birth, as the head passes through the birth canal.

• They also allow the brain to grow.
• An increased intracranial tension leads to the bulging of the anterior fontanelle.
• Similarly, depression of the anterior fontanelle indicates dehydration.
• One can easily draw the blood for testing or inject drugs in the superior sagittal sinus through anterior fontanelle.

The Posterior Aspect Of The Skull (Norma Occipitalis)

Bones Seen in Norma Occipitalis

• Right and left parietal bones.
• Squamous part of the occipital bone.
• Mastoid part of the right and left temporal bone.

Norma Basalis Interna

Sutures (Joints) Seen in Norma Occipitalis

• Posterior part of the sagittal suture in midline.
• The lambdoid suture between two parietal and occipital bones.
• Right and left parietomastoid sutures between the parietal and the mastoid part of the temporal bones.
• Right and left occipitomastoid sutures between occipital and mastoid bones.
• The parietal, occipital, and mastoid bones, on each side, meet at a point, which is known as an asterion. It is at a junction of the lambdoid, parietomastoid, and occipitomastoid sutures.

Features

• The external occipital protuberance is a palpable midline elevation. The highest point on this protuberance is also known as inion.
• The superior nuchal lines extend laterally from each side of the external occipital protuberance to the mastoid process.
• These lines mark the upper limit of the neck. The trapezius and sternocleidomastoid muscles are attached to this line.
• The external occipital crest descends downwards from the external occipital protuberance to the foramen magnum. It gives attachment to the ligamentum nuchae. The right and left inferior nuchal lines run laterally from the crest.
• The right and left highest nuchal lines are present just above the superior nuchal lines.
• These lines give attachment to the epicranial aponeurosis and the occipital belly of the occipitofrontalis.
• The mastoid foramen is situated close to the occipitomastoid suture and transmits an emissary vein and meningeal branch of the occipital artery.
• One or more sutural bones may be present at the lambda, lambdoid suture or at asterion.
• Between superior and inferior nuchal lines semispinalis capitis and obliquus capitis superior muscles are attached.
• Between the inferior nuchal line and posterior margin of the foramen, magnum rectus capitis posterior major and minor are attached.

Norma Basalis Interna

Anterior Aspect Of The Skull (Norma Frontalis)

This aspect of the skull forms the facial skeleton and consists of the forehead, orbits, nasal region, malar prominence, and upper and lower jaws.

Bones Seen in the Norma Frontalis

Identify the following bones from above downwards.

1. Frontal bone.
2. Nasal bones.
3. Zygomatic bones.
4. Maxillae.
5. Mandible.

The frontal bone and mandible are single bones, while nasal, zygomatic and maxillae are paired bones.

Sutures (Joints) Seen in the Norma Frontalis

Identify the following sutures, which are present close to the median plane:

• The frontonasal suture is present between the nasal process of the frontal bone and nasal bones.

• The front-maxillary suture is present between the nasal part of the frontal bone and the frontal process of the maxilla.
• The inter-nasal suture is present in the midline between two nasal bones above the nasal aperture.
• The naso-maxillary suture is present between the lateral border of the nasal bone and the frontal process of the maxilla.
• The inter-maxillary suture is present between the right and left maxilla below the nasal aperture.

Identify the following sutures present laterally in the norma frontalis:

• The fronto-zygomatic suture is present between the zygomatic process of the frontal bone and the frontal process of the zygomatic bone. This suture is present on the lateral border of the orbit.
• The zygomatico-maxillary suture is between the zygomatic process of the maxilla and the maxillary process of the zygomatic bone.
• The nasion is the meeting point of internasal and frontonasal sutures. It is present in the midline at the root of the nose.

Sulcus Chiasmaticus

Features of the Norma Frontalis

For ease of understanding norma frontalis is studied under the following headings:

Forehead

• The squamous part of the frontal bone forms the skeleton of the forehead. In the fetal and infant skulls the two halves of the frontal bone are separated by the frontal suture.
• Two frontal bones remain separated upto 6 years of age. In some adults, this suture may persist as a metopic suture.
• The glabella is the smooth, slightly depressed middle area just above the nasion.
• The superciliary arches are curved elevations above the medial part of supraorbital margins. They extend laterally from glabella.
• The frontal eminences are paired with rounded elevations above the superciliary arches.

Orbital Openings

Each orbital opening is quadrangular in shape and presents four margins.

• The supraorbital margin is formed by the frontal bone. This border presents a supraorbital notch or foramen at the junction of medial 1/3 with lateral 2/3.
• The supraorbital nerve and vessels pass to the forehead through the supraorbital notch or foramen. The supratrochlear vessels and nerve pass medial to the supraorbital notch.
• The infraorbital margin is formed by the maxilla medially and zygomatic bone laterally.
• The infraorbital foramen is present just below this margin, which transmits the infraorbital nerve and vessels.
• The lateral margin of the orbit is formed by the zygomatic and frontal bones.
• The medial margin is formed by the frontal bone and the frontal process of the maxilla.
• A detailed description of the orbital cavity is given later.

Malar Prominence

• The prominence of the cheek is formed by the zygomatic bone. It is situated inferolateral to the orbit.
• The zygomatico-facial foramen is present on the bone, which transmits the nerve of the same name. Anterior Nasal Aperture The nasal aperture is piriform in shape.
• It is bounded above by the right and left nasal bones, while lateral and inferior boundaries are formed by the nasal notches of the right and left maxilla.
• The anterior nasal spine is a median bony projection from the maxillae.
• Margins of the anterior nasal aperture give attachment to the nasal cartilage.
• In the depth of the anterior nasal aperture nasal septum can be seen in the midline. This septum separates the cavity of the nose into right and left nasal cavities. A detailed description of the nasal cavity.

Sulcus Chiasmaticus

Upper Jaw (Maxillae)

The upper jaw is formed by the right and left maxilla.

• The alveolar process of the maxilla bears the sockets for the upper teeth.
• The root of the canine tooth produces an elevation on the upper jaw, which is known as canine eminence.
• The canine fossa is situated just lateral to the canine eminence.
• The incisive fossa is situated above the incisor teeth.

Lower Jaw (Mandible)

The lower jaw is formed by the mandible.

• The mandible is the only movable bone of the skull.
• The alveolar processes house the lower teeth.
• The mental foramen is present below the 2nd premolÿr teeth. It gives passage to the mental nerve and vessels.
• The anterior surface of the symphysis menti presents a triangular elevation, the mental protuberance.

Attachment of Muscles in the Norma Frontalis

Students should study the attachment of muscles on the norma frontalis

The Orbital Cavity

We have already studied the orbital margin in this chapter. Here, we shall study the walls and various openings of the orbital cavity.

The orbit is like a four-sided pyramid. It has a base, an apex, a roof, a floor, a medial wall, and a lateral wall.

Sulcus Chiasmaticus

The Base

The base of the orbit is the orbital opening. It has four margins, i.e., upper, lateral, medial, and inferior margins.

The Apex

The apex of the orbit lies posteriorly.

The Medial Wall

The medial wall of the orbit, from anterior to posterior, is formed by the frontal process of the maxilla, lacrimal bone, orbital plate of the ethmoid, and body of the sphenoid.

• Most anteriorly the medial wall shows a deep groove called a lacrimal groove.
• This groove lodges the lacrimal sac. It is bounded anteriorly and posteriorly by the anterior and posterior lacrimal crests, respectively.
• Most of the medial wall is formed by the orbital plate of the ethmoid.
• The anterior and posterior ethmoidal foramina are present at the superior border of this bone.

The Superior Wall or Roof

The superior wall is formed mainly by the orbital plate of the frontal bone. Most posteriorly, a small part of the roof is also formed by the lesser wing of the sphenoid.

Anteromedially there is the presence of a small depression called the trochlear fossa, which gives attachment to the pulley for the superior oblique muscle.

Anterolaterally there is a deep fossa called as lacrimal fossa for lacrimal gland.

Skull Regions

The Lateral Wall

It is formed anteriorly by the zygomatic bone and posteriorly by the greater wing of the sphenoid.

The Inferior Wall or Floor

It is mainly formed by the maxilla. The small anterolateral part of the floor is also formed by the zygomatic bone. Most posteriorly the floor is formed by the orbital process of the palatine bone.

Fissures, Canals, and Foramina of the Orbital Cavity

The orbital cavity communicates with the neighboring regions of the skull through superior and inferior orbital fissures, optic and infraorbital canals, and various foramina.

It is present posteriorly between the roof and posteriorly with the pterygopalatine fossa lateral wall of the orbital cavity.

The Superior Orbital Fissure 

It is posteriorly between the infratemporal fossa. bounded above by the lesser wing of the fissure gives passage to the maxillary sphenoid, medially by the body of the sphenoid and Zygomatic nerves, emissary veins, and below and laterally by the greater wing infraorbital vessels. of the sphenoid.

The Inferior Orbital Fissures

It is present posteriorly between the lateral wall and the floor of the orbit. It is bounded above and laterally by the greater wing of the sphenoid and below and medially by the maxilla.

It communicates sphenoid and below and medially by the maxilla. It communicates The fissure gives passage to the maxillary and Zygomatic nerves, emissary veins, and infraorbital vessels.

Skull Regions

The Optic Canal

The Optic canal is present at the apex of the orbital cavity at the junction of the roof and medial wall. It is bounded medially by the body of the sphenoid and laterally by the lesser wing. It communicates with the middle cranial fossa and transmits the optic nerve along with its meningeal covering and ophthalmic artery. A common tendinous ring, which gives origin to four recti muscles of the eye, is attached surrounding the opening of the optic canal.

The Infraorbital Canal

The infraorbital canal is present in the bony substance of the maxilla. The canal is continuous posteriorly on the floor of the orbit as an infraorbital groove and opens anteriorly at the infraorbital foramen.

It gives passage to the infraorbital nerve and vessels. The infraorbital nerve is the continuation of the maxillary nerve.

Anterior and Posterior Ethmoidal Foramina

These two small foramina are present at the upper border of the orbital plate of the ethmoid (at the junction of the roof and medial wall of the orbit, These foramina transmit the anterior and posterior ethmoidal nerves and vessels to the anterior cranial fossa.

Skull Regions

The Lateral Aspect Of The Skull (Norma Lateralis)

This aspect of the skull is formed by cranial and facial bones. The posterosuperior region of norma lateralis (cranial part) includes the temporal fossa, external acoustic meatus, and mastoid part of the temporal bone.

The anteroinferior part of the norma lateralis (facial part) includes the zygomatic arch, infratemporal fossa, lateral aspect of the maxilla and mandible.

Bones Seen in the Norma Lateralis

Identify the following bones on the lateral aspect of the skull:

1. Frontal.
2. Parietal.
3. Occipital.
4. Nasal.
5. Maxilla.
6. Zygomatic.
7. Sphenoid.
8. Temporal
9. Mandible

Sutures (Joints) of the Norma Lateralis

Many sutures, which are seen in this aspect, have been already observed while studying norma frontalis, verticalis, and occipitalis. Hence, we shall study the sutures present in the central region of the norma lateralis.

H Shaped Suture

• The H-shaped suture is the meeting point of four bones, i.e., frontal, parietal, greater wing of the sphenoid, and squamous part of the temporal bone.
• A small circular area enclosing parts of all four bones is called a “pterion”.
• The pterion lies on the floor of the temporal fossa. The horizontal limb of the suture is the joint between the anteroinferior angle of the parietal bone and the greater wing of the sphenoid (parietosphenoid suture).
• The greater wing of the sphenoid articulates anteriorly with the frontal bone (at front sphenoidal suture) and posteriorly with the squamous part of the temporal bone (at temporosphenoidal suture).

The Parietosquamous and Parietomastoid Sutures

The lower border of the parietal bone articulates anteriorly with the squamous part of the temporal bone at parietosquattious suture and posteriorly with the mastoid bone at the parietomastoid suture.

Lambdoid Suture

At this suture, the posterior border of the parietal bone articulates with the occipital bone.

Occipitomastoid Suture

Here the occipital bone articulates with the mastoid part of the temporal bone. Features of the Norma Lateralis Following bony features are seen on the lateral aspect of the skull:

Skull Regions

Temporal Lines

Superior and inferior temporal lines are seen in this aspect. The superior line starts at the zygomatic process of the frontal bone. It arches upwards and backward crossing the coronal suture and fades away on the temporal bone.

It gives attachment to epicranial aponeurosis and temporal fascia. The inferior line starts along with the superior and runs inferior and parallel to it. Posteriorly, it runs downwards and forwards on the temporal bone to become continuous with the supramastoid crest.

The crest is further continuous anteriorly with the posterior root of the zygoma. The inferior temporal line limits the attachment of the temporalis muscle.

Zygomatic Arch

The zygomatic arch is formed by the articulation between the temporal process of the zygomatic and the zygomatic process of the temporal bone. At the posterior end and its lower border, the zygomatic arch bears a tubercle called as root of the zygoma.

Here the zygomatic arch divides into anterior and posterior roots. Trace the posterior root backwards along the lateral margin of the mandibular fossa, and then above the external acoustic meatus to become continuous with the supramastoid crest.

The anterior root passes horizontally as the articular tubercle, which lies anterior to the mandibular fossa.

The temporal fascia is attached to the upper border of the zygomatic arch. The lower border and inner surface of the arch give origin to the masseter muscle.

The External Acoustic Meatus

• The tympanic plate and squamous part of the temporal bone form the external acoustic meatus.
• The roof and upper part of the posterior wall are formed by squamous temporal bone, while the lower part of the posterior wall, floor, and anterior wall are by the tympanic plate.
• The margin of the meatus gives attachment to the cartilaginous part of the external acoustic meatus.

Supramental Triangle

It is a depression, situated postero-superior to the external acoustic meatus.

It is bounded above by the supra mastoid crest, in front by the posterosuperior margin of the external acoustic meatus, and behind by a vertical line drawn along the posterior margin of the meatus. Deep in this triangle lies the mastoid antrum.

Mastoid Process

The mastoid part of the temporal bone lies behind the external acoustic meatus. It is continuous above the squamous temporal bone.

The mastoid process is a downward conical projection from the mastoid part of the temporal bone. The asterion is the junctional point of three sutures, i.e., parietomastoid, occipital mastoid, and lambdoid.

The external surface of the mastoid provides attachment to the sternocleidomastoid, splenius capitis, and longissimus capitis muscles.

A mastoid foramen pierces the bone near the occipitomastoid suture. It transmits an emissary vein from the sigmoid sinus and the meningeal branch of the occipital artery.

Skull Regions

The Styloid Process

• The styloid process is seen when the skull is viewed from the lateral side. It is about a 2 to 5 cm long process projecting downwards, forwards, and medially.
• It is situated in front of the mastoid process on a deeper plane. It gives attachment to the styloglossus, stylohyoid, and stylopharyngeus muscles. The stylohyoid and stylomandibular ligaments are also attached to it.

Temporal Fossa

This is a shallow fossa that lies above the zygomatic arch. The temporalis muscle is located in this fossa.

This fossa is bounded:

• Posteriorly and superiorly by temporal lines.
• Anteriorly by the temporal surface of the frontal and zygomatic bones.
• Interiorly by the superior border of the zygomatic arch and supramastoid crest (on the lateral side). Interiorly on the medial side by the infratemporal crest of the greater wing of the sphenoid.
• Between zygomatic arch and infratemporal crest temporal fossa communicates below with the infratemporal fossa.
• Floor of the temporal fossa is formed by the part of the frontal, parietal, temporal and greater wing of the sphenoid bones. The circular area enclosing all these four bones and H shaped suture is called as pterion.
• It is situated 4 cm above the mid point of the zygomatic arch and 3.5 cm behind the frontozygomatic suture.
• The middle meningeal vein, anterior branch of middle meningeal artery, and stem of the lateral sulcus of brain lie deep to the pterion.
• The contents of the temporal fossa are temporalis muscle, deep temporal vessels and nerves and zygomaticotemporal nerve.

Infratemporal Fossa

It is an irregular fossa below the zygomatic arch and behind the maxilla. It communicates above with the temporal fossa deep into the zygomatic arch.

Boundaries

• Anterior wall: The posterior surface of the body of the maxilla bone. The surface of the maxilla shows many perforations (openings) for posterosuperior alveolar nerves and vessels.
• Medial wall: It is formed by the lateral pterygoid plate and pyramidal process of palatine bone. The junction of the anterior and medial walls shows a fissure called a term gomaxillaiy fissure. Deep to the fissure lies the pterygopalatine fossa.
• Lateral wall: It is formed by the ramus and coronoid process of the mandible.
• Roof: The roof is formed by the temporal surface of the greater wing of the sphenoid. At the junction of the roof and anterior wall, lies the lateral part of the inferior orbital fissure through which the infratemporal fossa communicates with the orbit Foramen ovale and foramen spinosum are present in the roof of the infratemporal fossa.
• Floor: It is not bounded but open.
• Posterior wall: It is also open.

The contents of the infratemporal fossa are as mentioned below:

• Lateral and medial pterygoid muscles and lower part of the temporalis.
• The maxillary artery and its branches, pterygoid venous plexus.
• Mandibular, maxillary and chorda tympani nerve and otic ganglion.

Skull Regions

Pterygopalatine Fossa

It is a small pyramidal space situated below the apex of the orbit and deep to the pterygomaxillary fissure.

Boundaries

Anterior: Posterior surface of the body of the maxilla.

Posterior: Root of the pterygoid process and the anterior surface of the greater wing of the sphenoid.

Medial: The perpendicular plate of the palatine bone.

Lateral: It is open and communicates with the infratemporal fossa through the pterygo¬ maxillary fissure. (The pterygomaxillary fissure is a triangular gap bounded anteriorly by the maxilla and posteriorly by the pterygoid process.

It transmits the third part of the maxillary artery, maxillary nerve, and posterior superior alveolar nerve and vessels).

Roof: Medially it is bounded by the body of the sphenoid and orbital process of the palatine bone. Laterally it communicates with the inferior orbital fissure.

Floor: It is closed due to the fusion of the anterior and posterior walls.

Communications of the Pterygopalatine Fossa

It communicates with the following:

• The orbit-Through the infraorbital fissure.
• The infratemporal fossa-Through pterygomaxillary fissure.
• The nasal cavity-Through sphenopalatine foramen.
• The middle cranial fossa-Through the foramen rotundum.
• The foramen lacerum—Through pterygoid canal.

Contents of the Pterygopalatine Fossa

• Maxillary nerve, pterygopalatine ganglion and its branches.
• The third part of the maxillary artery.

The Norma Basalis Externa

To visualize the base of the skull, it is necessary to detach the mandible from the rest of the skull. The base of the skull is formed, from anterior to posterior, by maxillae, palatine, vomer, sphenoid, temporal and occipital bones.

For the convenience of description, the norma basalis is divided into anterior, middle, and posterior parts by two imaginary horizontal lines.

The first imaginary horizontal line is drawn along the posterior border of the hard palate and the second line passes through the anterior margin of the foramen magnum.

Anterior Part of the Norma Basalis Externa

It is formed by the alveolar arch of the maxilla and hard palate.

Alveolar Arch

The alveolar arch is formed by the alveolar processes of the right and left maxillae. It is horseshoe-shaped and possesses the sockets for the roots of the teeth of the upper jaw.

Skull Regions

Hard Palate

• The hard palate lies within the alveolar arch.
• The anterior 2/3 of the hard palate is formed by the palatine processes of the right and left maxillae.
• The posterior 1/3 is formed by the horizontal plates of palatine bones.

Hard Palate Features

Sutures (joints) and foramina are seen in the anterior part of the norma basalis.

Intermaxillary, interpalatine, and palato maxillary sutures. All the above three sutures are collectively called cruciform sutures.

The Greater Palatine Foramen

• It is situated just medial to the third molar, posterior to the palatomaxillary suture.
• A groove rims forward from this foramen. This foramen transmits greater palatine vessels and nerves.

The Lesser Palatine Foramina

• These are two to three small foramina situated behind the greater palatine foramen. These foramina are present in the pyramidal process of the palatine bone.
• The lesser palatine vessels and nerves pass through these foramina. The Incisive Fossa It is a triangular depression in the median plane behind the central incisor teeth.
• The right and left lateral walls of the fossa bear lateral incisive foramen, which communicate with the floor of the nasal cavity. It gives passage to the nasopalatine nerve and greater palatine vessels.
• Pyramidal Process of the Palatine Bone It occupies the gap between the lower end of the medial and lateral pterygoid plates.

The Posterior Nasal Spine

It is a midline projection from the posterior border of the hard palate. It gives attachment to the musculus uvulae on each side.

Palatine Crest

It is a curved ridge a little in front of the posterior border of the hard palate. It gives attachment to the palatine aponeurosis and the tendon of tensor veli palatini.

Premaxilla

It is a triangular piece of maxilla holding four incisor teeth. In young persons a suture may be seen running from the posterior part of the incisive fossa laterally between the lateral incisor and canine teeth, separating the premaxilla from the rest of the maxilla.

The Middle Part of the Norma Basalis Externa

The middle part extends between two imaginary lines, i.e., the anterior line drawn along the posterior border of the hard palate and a posterior line drawn along the anterior margin of the foramen magnum.

The structures present in the region are divided into median areas and right and left areas.

The bones present in the median area, from anterior to posterior are

• The posterior border of the vomer.
• Body of sphenoid.
• Basilar part of the occipital bone.

The bones in the lateral area are:

• Medial and lateral pterygoid plates on the right and left side. These plates are the part of the sphenoid bone.
• The infratemporal surface of the greater wing of the sphenoid. It is situated lateral to the pterygoid plates.
• Temporal bone with its squamous, tympanic, and petrous parts.

Posterior Nasal Apertures and Related Structures Features

The Posterior Nasal Apertures and Related Structures These are quadrilateral in shape and situated above the posterior margin of the hard palate.

• The posterior border of the vomer separates the right and left apertures from each other, thus forming the medial boundary of each aperture.
• The superior surface of the horizontal plate of palatine bone forms the floor of the posterior nasal aperture.
• Laterally, each aperture is bounded by the perpendicular plate of palatine bone, which articulates with the medial pterygoid plate, posteriorly.
• The roof of the aperture is formed by the ala of the vomer and the sphenoidal process of the palatine bone.

The upper border of the vomer splits into two alae close to the inferior surface of the body of the sphenoid.

The midline groove between two alae of the vomer articulates with the sphenoidal rostrum (which is a midline ridge on the inferior surface of the body of the sphenoid).

The undersurface of the ala of the vomer, on each side, is overlapped by the vaginal process, which arises from the root of the medial pterygoid plate.

There exists a narrow vomer original canal between the undersurface of the ala of the vomer and the upper surface of the vaginal process.

It is present occasionally and gives passage to the pharyngeal vessels and nerves. From the upper end of the perpendicular plate of the palatine bone, there extends a sphenoidal process medially, which overlaps the undersurface of the vaginal process.

A narrow canal is present between the undersurface of the vaginal process and the superior surface of the sphenoidal process.

It is called as palatinovaginal canal and gives passage to the pharyngeal vessels and nerves. The vomerovaginal canal is situated posteriorly as compared to the palatinovaginal canal.

The Median Bar of Bone

• Just behind the alae of vomer bone there is the presence of a broad bar of bone in the midline. It extends upto the foramen magnum. It is formed by two bones, i.e.,
• Under the surface of the body of the sphenoid and basilar part of the occipital bone. These two bones (body of sphenoid and occipital bone) remain separated from each other by a cartilaginous synchondrosis joint which later fuses at about 25 years of age.
• A median elevation is seen just in front of the foramen magnum. It is known as the pharyngeal tubercle, which gives attachment to pharyngeal raphae and fibers of the superior constrictor.
• Note the attachment of longus capitis and rectus capitis anterior on the basilar part of the occipital bone.

Pterygoid Processes

• Each pterygoid process descends vertically downwards from the junction of the body and the greater wing of the sphenoid.
• The anterior surface of the root of the pterygoid process forms the posterior wall of the pterygopalatine fossa.
• The pterygoid process consists of medial and lateral pterygoid plates.
• The pterygoid plates unite anteriorly and enclose a fossa (pterygoid fossa), which faces posterolaterally.
• The anterior surface of the fused medial and lateral pterygoid plates form the posterior boundary of the pterygomaxillary fissure.
• At the lower end, a gap between medial and lateral pterygoid plates is occupied by the pyramidal process of the palatine bone

The Medial Pterygoid Plate

• Trace above the posterior border of the medial pterygoid plate. It ends in a small fossa the “scaphoid fossa”. It gives attachment to the tensor veli palatini.
• The lower end of its posterior border projects downwards and laterally as a hook, the hamulus. Around the hamulus, the tendon of tensor veli palatini turns medially to enter the soft palate. The hook of the hamulus also gives attachment to the pterygomandibular raphe.
• Its posterior border gives attachment to the pharynx basilar fascia.
• An angular process (process tubarius) projects backward from the middle of the posterior border of the medial pterygoid plate. This process supports the medial end of the auditory tube.
• The lower end of the posterior border with the pterygoid hamulus gives origin to the superior constrictor muscle.

The Lateral Pterygoid Plate

• The medial surface of the lateral pterygoid plate gives origin to the deep head of the medial pterygoid muscle.
• Its lateral surface gives origin to the lower head of the lateral pterygoid muscle.

Infratemporal Surface of the Greater Wing of Sphenoid

This surface of the greater wing of the sphenoid extends laterally from the root of the lateral pterygoid plate. It is pentagonal and forms the roof of the infratemporal fossa.

• Anteriorly it forms the posterolateral border of the inferior orbital fissure.
• Laterally the surface is limited upto the infratemporal crest. Beyond this crest, the greater wing extends to the temporal surface.
• Postero-laterally it articulates with the squamous part of the temporal bone.
• Posteromedially it articulates with the petrous part of the temporal bone. At the junction of these two bones, a sulcus is formed, which is known as sulcus tubae.

The sulcus lodges the cartilaginous part of the auditory tube

The posterior-most of this bone projects down as the spine of the sphenoid.

The spine of the sphenoid gives attachment to:

Ligaments-Sphenomandibular, pterygospinous, and anterior ligament of the malleus.

Muscles-Posterior fibers of tensor veli palatine.

Related structures- Auriculotemporal nerve (laterally) chorda tympani nerve and auditory tube (medially).

The infratemporal surface of the greater wing of the sphenoid gives origin to the upper head of the lateral pterygoid muscle.

This surface presents two foramina, i.e., foramen ovale and spinosum. The foramen ovale is oval and presents posterolateral to the root of the lateral pterygoid plate. Foramen spinosum is small rounded foramen situated posterolateral to foramen ovale.

It is present anteriomedial to the spine of the sphenoid. Sometimes a small foramen may be seen medial to the foramen ovale, emissary sphenoidal foramen.

The Infratemporal Surface of the Squamous Part of the Temporal Bone This part is present posterolateral to the greater wing of the sphenoid and along with the infratemporal surface of the greater wing of the sphenoid it also forms the roof of the infratemporal fossa.

When a zygomatic process is traced backward this surface presents a tubercle (tubercle of the root of zygoma) where the zygomatic process divides into anterior and posterior roots.

The anterior root runs medially anterior to the mandibular fossa and bears an articular tubercle.

The posterior root forms the lateral boundary of the mandibular fossa. Behind the articular tubercle, the mandibular fossa is deep depression.

Both the articular tubercle and mandibular fossa, are articular and articulates with the head of the mandible.

The posterior part of the mandibular fossa is non-articular and formed by the tympanic plate of the temporal bone.

The Tympanic Part of the Temporal Bone

• The tympanic plate forms the anterior wall, floor, and lowermost part of the posterior wall of the external acoustic meatus.
• The squamous part of the temporal bone and tympanic plate unite with each other at the squamotympanic fissure, which is present on the floor of the mandibular fossa.
• The tegmen tympani part of the petrous temporal bone may project in the medial part of the squamotympanic fissure.
• The presence of the tegmen tympani divides the squamotympanic fissure into a petrosquamous fissure and a petrotympanic fissure.
• The petro-tympanic fissure gives passage to chorda tympani nerve, anterior tympanic artery and anterior ligament of malleus.

The Inferior Surface of Petrous Part of the temporal bone

The petrous part of the temporal bone is situated behind the greater wing of the sphenoid and lateral to the body of the sphenoid and basilar part of the occipital bone.

The apex of the bone is separated from the body of the sphenoid, the root of the pterygoid process, and the basilar part of the occipital bone by the foramen lacerum.

The carotid canal opens in the posterior wall of the foramen lacerum, while the pterygoid canal opens into its anterior wall. The upper part of the foramen lacerum is traversed by the internal carotid artery.

The nerve to the pterygoid canal is formed in the foramen lacerum by the union of the greater superficial petrosal and deep petrosal nerves. The nerve then passes through the pterygoid canal and enters the pterygopalatine fossa.

A quadrilateral area behind the apex of the petrous bone gives origin to tire levator veli palatini.

The lower opening of the carotid canal is situated just behind the quadrilateral area the inferior surface of the petrous temporal bone.

It transmits the internal carotid artery. Posterior to the lower opening of the carotid canal there lies the jugular fossa.

The sulcus tube is a groove, which lies between the posteromedial margin of the greater wing of the sphenoid and the petrous part of the temporal bone. It is occupied by the cartilaginous part of the auditory tube.

The Posterior Part of the Norma Basalis Externa

• The posterior part lies behind the imaginary line drawn along the anterior margin of the
  foramen magnum. This part is also divided into median area and two lateral areas:
• The median area consists of the foramen magnum and the squamous part of the occipital bone behind it.
• The condylar parts of the occipital bone are present on either side of the foramen magnum.
• The basilar part of the occipital bone lies anterior to the foramen magnum The bones in the lateral area, on each side, are the mastoid and styloid process.

The Median Area

The foramen magnum is large and oval. It connects the posterior cranial fossa above with the vertebral canal below.

The Basilar Part

The basilar part of the occipital bone is in The basilar part of the occipital bone is in sphenoid bone. These two bones are separated from each other by a primary cartilaginous joint in young but fuse in adults.

The pharyngeal tubercle is a small tubercle present on the inferior is a small tubercle present on the inferior attachment to the pharyngeal raphe.

The Foramen Magnum

The alar ligaments, which are attached to the lateral margins of the foramen magnum, divide the foramen into small anterior and large posterior parts.

The structures passing through the anterior and posterior parts are shown. The anterior and posterior margins of the foramen magnum give attachment to the anterior and posterior atlanto-occipital membranes respectively.

The Condylar Parts

The condylar parts of the occipital bone consist of right and left occipital condyles, which are situated on each side of the foramen magnum. The jugular process is present lateral to each condyle. The condyles are set obliquely and their inferior surface is convex and articular.

Each condyle articulates with the corresponding upper surface of the lateral mass of the atlas vertebra (superior articular facet) to form an atlantooccipital joint.

There is an opening of the hypoglossal or anterior condylar canal on the lateral border of the condyle near its anterior end. It gives passage to the hypoglossal nerve, emissary vein, and meningeal branch of the ascending pharyngeal artery.

A condylar fossa is present posterior to each condyle which may show the presence of a canal which may show the presence of a canal to the emissary vein which connects the sigmoid sinus to occipital veins.

The jugular process articulates laterally with the petrous temporal bone by a primary cartilaginous joint. The anterior margin of the jugular process is free and known as the jugular notch. The jugular notch forms the posterior boundary of the jugular foramen.

The Jugular Foramen

• This irregular large foramen is bounded anteriorly by the posterior border of the petrous temporal bone and posteriorly by the jugular notch of the jugular process of the occipital bone.
• It is divided into anterior, middle, and posterior parts. The posterior part of the jugular foramen presents a jugular fossa, which is due to the presence of depression in the petrous temporal bone.
• The mastoid canaliculus is an opening of a minute canal in the lateral wall of the jugular fossa which transmits the auricular branch of the vagus.
• The tympanic canaliculi are present on the ridge between the jugular fossa and the lower opening of the carotid canal. The structures pass through three divisions of the jugular foramen.

The Squamous Part ligament

This part lies behind the foramen magnum. In the midline, there extends an external occipital crest between the foramen magnum and the external occipital protuberance.

The upper end of the ligamentum nuchae is attached to the crest and protuberance. The superior and inferior nuchal lines and attachment of muscles in this area have already been described in “norma occipitalis”.

The Lateral Area

• In the lateral area, there are three important structures, i.e., styloid process, mastoid process, and stylomastoid foramen.
• Styloid Process It is a long conical process, which projects downwards, forwards, and medially below the tympanic part of the temporal bone.
• It lies lateral to the jugular fossa.
• It gives attachment to 3 muscles and two ligaments.
• It is related laterally to the parotid gland and medially to the internal jugular vein.
• Near its base, it is crossed by the facial nerve.

Mastoid Process

• It is a conical projection from the mastoid part of the temporal bone. The mastoid process is situated posterolateral to the styloid process.
• A deep groove (digastric groove) is seen on its medial aspect, which gives attachment to the posterior belly of the digastric muscle.

Stylomastoid Foramen

The stylomastoid foramen is present between styloid and mastoid processes, i.e., posterolateral to the styloid process and anteromedial to the mastoid process. The stylomastoid artery and facial nerve pass through it.

The Interior Of The Skull

• When the upper part of the vault of the skull (skull cap or calvaria) is removed we may see the inner surface of the cranial vault and the interior of the base of the skull.

Inner Surface of the Cranial Vault

• The various bones and the intervening sutures forming the cranial vault are the same as observed in the norma verticalis.
• The frontal crest is the midline structure present most anteriorly
• A groove extends anteroposteriorly in the median plane, from the frontal crest to the internal occipital protuberance. This groove is known as the sagittal sulcus.
• The superior sagittal sinus is lodged in the sagittal sulcus. At the internal occipital protuberance, this sinus becomes continuous with the right transverse sinus.
• The frontal crest and the margins of the sagittal sulcus give attachment to the falx cerebri.
• Many small depressions {granular pits) are observed on each side of the sagittal sulcus. These are produced by the arachnoid granulations. Their number increases with the increasing age.
• Note the presence of parietal foramen on either side of the sagittal suture about 3.5 cm anterior to lambda. These foramina transmit emissary veins.
• The inner aspect of the calvaria shows the presence of grooves for the meningeal vessels. These grooves run backward and upwards from the anteroinferior angle of the parietal bone.

Interior of the Base of the Skull

The internal aspect of the base of the skull (norma basalis internal) as seen after the removal of the skull cap, can be divided into three fossae, i.e., anterior, middle, and posterior cranial fossae

The Anterior Cranial Fossa

Bones of the Anterior Cranial Fossa The anterior cranial fossa is formed by the frontal bone, cribriform plate of the ethmoid, lesser wing of the sphenoid, and the anterior part of the superior surface of body of the sphenoid (jugum sphenoidal).

Sutures of the Anterior Cranial Fossa

With the help of identifying frontoethmoidal, frontosphenoidal, and sphenoethmoidal sutures.

Borders

The anterior and lateral boundaries of the fossa are formed by the frontal bone.

The posterior boundary is formed by the posterior border of the lesser wing of the sphenoid, the anterior clinoid process, and the anterior border of the sulcus chiasmaticus.

Floor

In the median region, the floor is formed by the cribriform plate of ethmoid and jugum sphenoidal.

While, the lateral region of the floor is formed by the orbital plates of the frontal bone and the lesser wings of the sphenoid, on each side.

Median Area of the Floor

• The most anterior structure in the midline is the frontal crest.
• Posterior to the frontal crest a triangular process, the crista galli, is seen. It projects upwards from the cribriform plate and provides attachment to the falx cerebri.
• Between the frontal crest and crista galli identify the foramen caecum. Sometimes it transmits a vein from the nasal mucosa to the superior sagittal sinus.
• The cribriform plate of ethmoid is present on either side of the crista galli between the orbital plates of the frontal bone. The cribriform plate separates the anterior cranial fossa from the nasal cavity.
• It presents many small apertures through which pass the olfactory nerves from the nasal mucosa to the olfactory bulb.
• On each side of the cribriform plate, there is an opening of the anterior and posterior ethmoidal canals.
• The anterior canal transmits anterior ethmoidal vessels and nerves, while the posterior canal transmits only posterior ethmoidal vessels.
• Posterior to the cribriform plate the median area of the floor is formed by jugum sphenoidale of the body of the sphenoid. It forms the roof of the sphenoidal air sinus. Lateral Area of the Floor On each side it consists of an orbital plate and a lesser wing of the sphenoid.
• The orbital plate of the frontal bone lies lateral to the cribriform plate on either side. It is convex and shows the impre¬ ssions of cerebral gyri.
• Laterally it forms the roof of the orbit and medially the roof of the ethmoidal sinuses. Posteriorly, the orbital plates articulate with the anterior margin of the lesser wing of the sphenoid.
• The lesser wings of the sphenoid are continuous with the jugum sphenoidale medially. The posterior margin of the lesser wing is free and concave. It is related to the sphenoid-parietal sinus.
• The medial end of the posterior margin ends into the anterior clinoid process, which gives attachment to the free margin of tentorium cerebelli.

Middle Cranial Fossa

The middle cranial fossa is narrow in the middle and expanded laterally. It lodges hypophysis cerebri in the middle and temporal lobes of the brain on each side.

Boundaries

• The anterior boundary of the middle cranial fossa separates the anterior and middle fossae from each other.
• It is formed by the posterior border of the lesser wing of the sphenoid, anterior clinoid process and anterior border of the sulcus chiasmaticus.
• The posterior boundary separates it from the posterior cranial fossa.
• It is formed by the superior border of the petrous part of the temporal bone, posterior clinoid process, and dorsum sellae.
• On each side, the middle cranial fossa is bounded by the greater wing of the sphenoid, the squamous part of the temporal bone, and the parietal bone.

The floor of the Middle Cranial Fossa

It is shaped like a butterfly and consists of median and lateral parts.

Median Part of the Floor of the Middle Cranial Fossa

• The median part is formed by the body of the sphenoid. Most anteriorly sulcus chiasmaticus is present.
• It is a transverse groove, which becomes continuous laterally with the optic canal. The optic chiasma lies posterior to this groove.
• Each optic canal opens into orbit thus connecting the middle cranial fossa with orbit.
• It is bounded by anterior and posterior roots of the lesser wing and body of the sphenoid. This canal gives passage to the optic nerve, meninges, and ophthalmic artery.
• Behind the sulcus chiasmaticus, a saddle-shaped depression is present on the superior surface of the body of the sphenoid. It is known as sella turcica.
• The sella turcica consists of tuberculum shellac, hypophyseal fossa, and dorsum sellae from anterior to posterior. The tuberculum sellae is the median elevation just behind the sulcus chiasmaticus.
• It receives the attachment of the anterior margin of the diaphragm sellae. The hypophyseal fossa is a deep depression posterior to the tuberculum sellae. It lodges hypophysis cerebri. Deep to the hypophyseal fossa lies the sphenoidal air sinus.
• The dorsum sellae is a square-like vertical plate of bone posterior to the hypophyseal fossa. The superior border of the dorsum sellae, on each side forms the posterior clinoid process which gives attachment to the attached margin of the tentorium cerebelli. While the superior border itself gives attachment to the posterior margin of diaphragma sellae.

• On each side of the body of the sphenoid, there is the presence of a shallow groove called a carotid groove. This groove extends from the foramen lacerum to the medial side of the anterior clinoid process. It lodges the internal carotid artery.

Lateral Part of the Floor of Middle Cranial Fossa

Laterally the floor of the middle cranial fossa is formed by three bones, i.e., the cranial surface of the greater wing of the sphenoid, and squamous, and petrous parts of the temporal bone. Following fissures, foramina, and grooves are observed on the floor of the fossa.

The superior orbital fissure is a triangular oblique cleft present most anteriorly in the middle cranial fossa. It connects the middle fossa with the orbit.

The fissure is bounded above by the lesser wing of the sphenoid, below by the greater wing, and medially by the body of the sphenoid.

We have already seen that the fissure is divided into three parts by the attachment of a tendinous ring on the orbital surface of the fissure. The structures pass through three subdivisions of the superior orbital fissures.

The foramen rotundum is situated in the greater wing of the sphenoid just inferomedial to the medial end of the superior orbital fissure.

It opens anteriorly into the pterygopalatine fossa and transmits the maxillary nerve.

The foramen ovale is situated in the greater wing of the sphenoid posterolateral to the foramen rotundum. It opens into the infratemporal fossa and transmits the mandibular nerve.

The foramen spinosum is also present in the greater wing of the sphenoid, posterolateral to the foramen ovale, and communicates with the infratemporal fossa.

It gives passage to the middle meningeal artery and other structures.

Sometimes the emissary sphenoidal foramen is present between foramen rotundum and foramen ovale.

It transmits the emissary vein. Similarly, sometimes a foramen is present between foramen ovale and spinosum, which transmits lesser petrosal nerve. It is called as foramen innominatum.

The foramen lacerum is situated posteromedial to foramen ovale, between the body of the sphenoid and the apex of the petrous temporal bone.

The carotid canal opens in its posterolateral part. The carotid artery traverses the upper part of the foramen lacerum. The pterygoid canal opens in its anterior margin and gives passage to the nerve of the pterygoid canal.

In the lateral part of the floor, the markings of the middle meningeal vessels are seen. The groove runs forward and laterally from the foramen spinosum and later divides into two anterior and posterior branches of the middle meningeal artery.

The anterior surface of the petrous temporal bone forms the posterior wall of the middle cranial fossa. Near the apex, a shallow depression is seen. It is known as trigeminal impression for the trigeminal ganglion.

Arcuate eminence is a prominent elevation deep to which lies the superior semicircular canal.

The area lateral to the eminence is formed by the thin plate of bone called tegmen tympani.

This forms the roof of the middle ear cavity and auditory tube. The anterior surface of the petrous temporal bone presents two grooves running downwards and medially.

The upper and medial groove begins at the hiatus for the greater superficial petrosal nerve and runs towards the foramen lacerum. It lodges a greater superficial petrosal nerve.

The lower and lateral groove begins at the hiatus for the lesser petrosal nerve and runs towards the foramen ovale.

It lodges lesser petrosal nerves.

The superior border of the petrous bone is grooved for the lodgement of the superior petrosal sinus. Near the apex of the petrous temporal bone, this border is 184 crossed by the trigeminal nerve. This border also gives attachment to the tentorium cerebelli.

Posterior Cranial Fossa

The posterior cranial fossa is the deepest of the three fossae and lodges the hindbrain (cerebellum, pons, and medulla).

Bones Forming the Posterior Cranial Fossa

• Posterior part of the body of the sphenoid.
• Occipital bone.
• The posterior surface of the petrous temporal bone.
• Mastoid part of the temporal bone.
• Posteroinferior angle of parietal bone.

Sutures and Fissures of the Posterior Cranial Fossa

• The lower end of lambdoid suture between parietal and occipital bone.
• The parieto-mastoid suture.
• The occipito-mastoid suture.
• Petro-occipital suture.

Boundaries

The middle and posterior cranial fossa are separated from each other by the dorsum sellae, posterior clinoid process, and superior border of the petrous temporal bone.

On the lateral side, this fossa is bounded by the mastoid part of the temporal bone and the postero-inferior angle of the parietal bone.

Posteriorly, it is bounded by the squamous part of the occipital bone. The Floor of the Posterior Cranial Fossa The floor can be divided into median and lateral parts.

The Median Part of the Floor

The median part of the floor presents the most striking structure, i.e., the foramen magnum.  The part anterior to the foramen magnum is called as clivus. The parts posterior to the foramen magnum are the internal occipital crest and internal occipital protuberance.

• The clivus is the sloping surface of the bone formed by the fusion of the basal part of the occipital bone and the body of the sphenoid.
• The lateral border of the basilar part of the occipital bone is separated by the petrous temporal bone by a petrooccipital fissure, which lodges the inferior petrosal sinus.
• The basilar part of the clivus gives attachment to the membrane tectoria, the upper band of the cruciate ligament, and the apical ligament of dens.
• The foramen magnum is a large oval-shaped central opening on the floor of the posterior fossa. Structures passing through this foramen.
• On each side of the foramen magnum, the inner opening of the hypoglossal canal lies just above its lateral margin. It transmits the hypoglossal nerves and vessels. The jugular tubercle is situated between the jugular foramen and the hypoglossal canal.
• It is related to the 9th, 10th, and 11th cranial nerves. Sometimes the posterior condylar canal is also present behind the jugular foramen and lateral to the jugular tubercle. It transmits the emissary vein.
• The internal occipital crest is a ridge present in the midline, which extends between the foramen magnum and internal occipital protuberance. It gives attachment to the falx cerebelli.
• The internal occipital protuberance is situated opposite the external occipital protuberance. On each side, it is related to the transverse sinus. It is also related to the confluence of dural venous sinuses.

The Lateral Part of the Floor

• The posterior surface of the petrous temporal bone, in its middle, shows the opening of the internal acoustic meatus.
• It transmits the facial and vestibulocochlear nerves and labyrinthine vessels. Posterolateral to the internal meatus there lies an oblique slit which leads upwards into a canal called the aqueduct of the vestibule. It lodges succus and ductus endolymphaticus.
• The right and left transverse sulci run laterally from each side of the internal occipital protuberance. The right sulcus is more prominent. The transverse sulcus lodges the transverse sinus.
• Each transverse sulcus curves downwards at the mastoid angle of the parietal bone as the sigmoid sulcus. The sigmoid sulcus runs downwards and medially with an S-shaped curve.
• It grooves the petrous and mastoid part of the temporal bone to reach the posterior end of the jugular foramen.
• The jugular foramen is situated between the posterior end of the petro-occipital fissure and the terminal end of the sigmoid sulcus Above it is bounded by the petrous temporal bone and below by the jugular process of the occipital bone. It is divided into anterior, middle, and posterior parts.

Nasal Cavity

The nasal cavity is divided into right and left halves by vertical median septum (i.e., the nasal septum). Each half of the cavity consists of an anterior opening, i.e., the anterior nasal aperture, a posterior nasal aperture, a lateral wall, a medial wall, a roof, and a floor.

Anterior and Posterior Nasal Apertures

The anterior nasal apertures open on the norma frontalis, while both posterior nasal apertures open on the base of the skull just above the posterior margin of the bony palate.

The Medial Wall

The medial wall, anterosuperiorly, is formed by the perpendicular plate of the ethmoid. While posteroinferiorly it is formed by the vomer bone. In the living condition, the anterior gap in the bony septum is filled by septal cartilage.

The Lateral Wall

The lateral wall is formed by three irregular bony projections, i.e., superior, middle, and inferior conchae.

These conchae run anterol posteriorly and lie one above the other. The spaces deep into the conchae are called meatuses, i.e., superior, middle, and inferior meatuses. The area above the superior concha is called a sphenoethmoidal recess. The following bones form the lateral wall of the nose.

• Ethmoid—The superior and middle conchae are part of the ethmoid bone.
• The inferior concha is a separate bone.
• Perpendicular plate of the palatine bone.
• Maxilla—All the above three bones are attached to the nasal surface of the maxilla.
• A part of the nasal surface of the maxilla remains free on the anterior and inferior part of the lateral wall of the nose

Roof

From anterior to posterior, the roof is formed by nasal bone, frontal bone, cribriform plate of the ethmoid, anterior surface of a body of the sphenoid, and ala of the vomer.

The nasal cavity communicates with the anterior cranial fossa through numerous apertures in the cribriform plate of the ethmoid bone.

Floor

It is formed by the palatine process of It is formed by the palatine process of In the anterior part of the floor there is the upper opening of the incisive canal.

Further Details of Lateral Wall

Sphenoethmoidal Recess

It is situated above the superior concha and receives the opening of the sphenoid air sinus.

Superior Meatus

It is situated between the superior and middle conchae. It receives the opening of the posterior ethmoidal sinuses.

Middle Meatus

It is situated between the middle and inferior conchae. Deep to middle concha is a rounded prominence called the bulla ethmoidale.

It is produced by the middle ethmoidal air sinuses. The middle ethmoidal sinuses open on the bulla.

Antero-inferior to the bulla is a curved plate of bone called an uncinate process. It runs downwards and backward. The curved space between the uncinate process and bulla is called hiatus semilunaris. The hiatus semilunaris is continuous above and anteriorly into the infundibulum.

The infundibulum is continuous with the frontal air sinus. The anterior ethmoidal sinus also opens in the infundibulum. The maxillary air sinus opens behind the bulla at the posterior end of the hiatus semilunaris.

Inferior Meatus

It is present deep into the inferior concha and receives the opening of the nasolacrimal duct.

Sphenopalatine Foramen is present behind the superior concha and transmits the sphenopalatine artery and nasal branches of the pterygopalatine ganglion.

Skull Of The Newborn

The size of the cranium (brain box) is larger as compared to the facial skeleton. The brain box (calvaria) is large because of the rapid growth of the cerebrum.

The bones of the vault are ossified in membrane while the bones of the base of the skull are ossified in cartilage.

The size of the face at birth is small due to the following facts:

Norma Frontalis

• The glabella and superciliary arches are not well developed.
• The frontal bone is present in two halves, i.e., right and left separated by frontal suture.
• Small size of mandible and maxilla.
• Rudimentary maxillary air sinus.
• Non-eruption of teeth.
• The small size of the nasal cavity.
• The germs of developing teeth in the superior alveolar process are near the orbital floor.
• The paranasal sinuses are rudimentary or absent.
• The two halves of the mandible are united by the fibrous tissue at symphysis menti. These halves join each other at the end of the first year.

The Base Of The Cranium

• The cranial base is relatively short.
• Occipital and sphenoid bones are joined with each other by the cartilaginous joint.
• The squamous, lateral, and basilar parts of the occipital bone are separated from each other.
• The styloid process is not fused with the temporal bone.
• The mandibular fossa is flat and its articular tubercle is underdeveloped.
• The stylomastoid foramen is exposed on the lateral surface.

The Lateral View

• The mastoid process is absent
• The tympanic plate is represented by a C-shaped plate.
• The tympanic membrane is attached obliquely and exposed as the bony part of the external acoustic meatus is yet not developed.
• The cavities of the internal ear, middle ear, Lateral View Anterior fontanelle mastoid antrum, and three ear ossicles are of adult size at birth. However, the petrous temporal bone is much smaller.
• The angle of the mandible is obtuse 140 degrees
• The coronoid process is above the level of the head of the mandible

Norma Verticalis

• The bones of the vault are ossified in the membrane.
• The angles of the parietal bones are still membranous. Thus there are six fontanelles at four angles of both the parietal bones.
• The unpaired median fontanelles are called anterior and posterior fontanelles.
• Two lateral pairs of fontanelles are sphenoidal and mastoid fontanelle.
• The anterior fontanelle lies at the junction of sagittal, coronal, and frontal sutures.
• The posterior fontanelle lies at the junction of sagittal and lambdoid sutures.
• The sphenoidal and mastoid fontanelles are at the sphenoidal and mastoid angles of the parietal bones.

Anterior Fontanelle

The anterior fontanelle is present at the junction of frontal, coronal, and sagittal sutures hence, diamond-shaped. It measures about 4 cm in anteroposterior and 2.5 cm in transverse dimensions.

Deep to the anterior fontanelle lies superior sagittal sinus. It is usually closed between 18 months and 2 years of age.

Clinical Significance

• The bulging of the fontanelle indicates increased intracranial pressure.
• The depressed fontanelle indicates dehydration.
• As the superior sagittal sinus lies just deep to it blood can be withdrawn from the sinus.
• The intravenous transfusion of fluid or drugs is also possible through the superior sagittal sinus.
• The CSF can also be withdrawn from the lateral ventricle of the brain. For this a needle is introduced downwards and laterally at the lateral angle of the fontanelle.
• The fact, that the anterior fontanelle closes by the age of 2 years, is utilized to determine the age of the child.
• At the time of birth, fontanelle allows some overlap of the bones of the cranial vault. This helps in the reduction in the size of the foetal head during birth.

Hyoid Bone

Hyoid is a U-shaped bone present in the upper part of the neck.

It is not attached to any other bone but hangs at the level of the 3rd cervical vertebra with the help of muscles and ligaments. The hyoid bone consists of a central body and greater and lesser cornua.

Hyoid Bone Body

The body is rectangular and has an anterior and a posterior surface.

The anterior surface is convex and faces anterosuperiorly. A median ridge divides it into right and left halves. The posterior surface is concave and smooth.

Hyoid Bone Greater Cornua

Each end of the body is continuous posterolaterally as greater cornu. The greater cornu is flattened. It has two surfaces (upper and lower) and two borders (medial and lateral). The posterior end of the greater cornu is enlarged to form a tubercle.

Hyoid Bone Lesser Cornua

The lesser cornua are small conical projections attached to the bone at the junction of the body and greater cornu on each side.

Each cornu projects upwards and laterally. The lesser cornu may form a synovial joint with the greater cornu.

Hyoid Bone Particular Features

Attachments of muscles on the anterosuperior aspect are shown. Attachments of ligaments and membranes.

Hyoid Bone Ossification

The hyoid bone ossifies in cartilage by six centers. One center appears in each greater cornua at the end of intrauterine life. Soon after birth two centers appear for the body. One center appears in each lesser cornua at puberty.

Cervical Vertebrae

The cervical part of the vertebral column is highly mobile and its curvature is convex anteriorly. It is made up of 7 cervical vertebrae. A cervical vertebra is characteri¬ zed by the presence of a foramen in each transverse process (foramen transversarium). The 1st, 2nd, and 7th vertebrae are atypical, while 3rd to 6th vertebrae are typical.

Typical Cervical Vertebrae

A typical cervical vertebra consists of a body and vertebral arch. The body and vertebral arch enclose a vertebral foramen, which lodges the spinal cord and its meninges.

Cervical Vertebrae Body

• The body of the cervical vertebra is the smallest among all vertebrae. The shape of the cervical vertebra is oval, its anteroposterior diameter is less than side to side.
• The superior surface of the body is concave from side to side because of the presence of an upward-projecting lip on either side.
• The inferior surface is convex from side to side. The anterior border of the inferior surface projects downwards as a lip.
• The bodies of the adjacent vertebrae are connected by the intervertebral disc and a pair of synovial unconvertebral joints on each side of the disc.
• The vertebral foramen is large and triangular.

Vertebral Arch

It consists of pedicles, laminae, superior and inferior articular processes, transverse processes, and spine

Pedicles

These are rounded bars that arise from the posterolateral part of the body. They are directed backward and laterally hence, the vertebral foramen is large and triangular.

Lamina

Laminae are thin plates of bone. They are directed backward and medially from pedicles to meet each other in the midline at the base of the spinous process.

Spinous Process

It is short and bifid.

Articular Process

• The superior and inferior articular processes are present at the junction of pedicles and laminae and form a continuous articular pillar.
• The superior articular facet faces upwards and backward while the inferior facet faces downwards and forwards.
• The superior articular process articulates with the inferior articular process of the above vertebra.
• Between superior and inferior articular facets articular process is in the form of a bar and is known as an articular pillar.
• Besides bodies, the articular processes (articular pillar) also carry a considerable load on the head and neck.

Transverse Processes

• These are short and directed laterally. Each transverse process bears a foramen transversarium.
• Each process presents anterior and posterior roots (anterior and posterior to the foramen), anterior and posterior tubercles (at the lateral end of anterior and posterior roots), and an intertubercular bar (costotransverse bar) which is present lateral to the foramen.
• The anterior root, anterior tubercle, intertubercular bar and posterior tubercle represent the costal element (element of rib). The posterior root represents the true transverse process.
• The foramen transversarium of the cervical vertebrae (except C7) transmits the vertebral artery, sympathetic nerve plexus, and vertebral vein.
• The upper surface of the costotransverse bar is grooved and lodges the ventral ramus of the corresponding cervical nerve.

The First Cervical Vertebra

The first cervical vertebra is also known as the atlas.

It is easily identified from the rest of the other cervical vertebrae because:

• It is ring-shaped.
• It has nobody.
• It is the widest of all other cervical vertebrae.
• It has no spinous process.

The bone has two large masses (lateral masses) joined anteriorly by a short anterior arch and joined posteriorly by a much longer posterior arch.

The superior surface of each lateral mass bears an elongated kidney-shaped concave articular facet for articulation with the occipital condyle (to form atlanto-occipital joint).

Anatomical Position

Hold the bone in such a way that the concave superior articular surface of the lateral masses faces upwards. The short anterior arch should face anteriorly.

General Features

Lateral Mass

• Each lateral mass has a superior articular facet and an inferior articular facet. The superior facet is concave and kidney-shaped. The inferior facet is oval and flat.
• The inferior facet faces downwards and medially and articulates with the superior articular surface of the axis (2nd cervical vertebra) to form the lateral atlantoaxial joint.
• The medial surface of each lateral mass bears a tubercle for the attachment of the transverse ligament of the atlas.

The Anterior Arch

• It shows the presence of a small anterior tubercle in the midline.
• An oval articular facet is present on the posterior surface in the midline. This facet articulates with the dens of the 2nd cervical vertebra to form the median atlantoaxial joint.

The Posterior Arch

• The posterior arch is much longer than the anterior and bears a posterior tubercle on its posterior surface in the midline. It represents the rudimentary spinous process.
• There is the presence of a shallow groove on its superior surface posterior to each lateral mass. The groove lodges the vertebral artery and the first cervical spinal nerve.

The Transverse Process

The transverse process projects laterally from the lateral mass. It has foramen transversarium which transmits vertebral artery, vein, and sympathetic nerve.

Particular Features

• Attachments of ligaments, membranes, and muscles.
• Relations of blood vessels and nerves are
• The Second Cervical Vertebra proc.
• This vertebra is also known as the axis. It can be easily identified from the rest of the vertebrae because of the presence of dens or odontoid processes.
• The den is a blunt conical tooth-like process that projects superiorly from the body. The spinous process is long, strong, and bifid and projects posteriorly.

Anatomical Position

Hold the bone in such a way that the body of the vertebra lies anteriorly and the odontoid process faces upwards. The bifid spinous process should face posteriorly.

General Features

• The odontoid process is about 1.5 cm long. Its anterior surface bears a small oval facet for articulation with the anterior arch of the atlas. The posterior surface shows a groove, which lodges the transverse ligament of the atlas.
• The upper end of the body bears dens, while the lower surface articulates with the third cervical vertebra through the vertebral disc.
• Superior articular facets are situated lateral to the odontoid process. These are large oval facets, that articulate with the corresponding inferior facets of the atlas vertebra. Each facet is sloping and partly situated on the body and partly on the pedicle.
• The transverse processes are small and lie lateral to the superior articular facets.
• The pedicle, lamina, and spine are massive and very strong. The spine is bifid.
• The inferior articular process is present at the junction of the pedicle and lamina. Its articular facet faces downwards and forwards.

Seventh Cervical Vertebra

• This vertebra is easily identified from the other cervical vertebrae due to the presence of a very long, horizontal spinous process, which is not bifid (ends in a single tubercle).
• As the tip of the spinous process (tubercle) can be easily felt under the skin it is also called vertebra prominence. The transverse processes are large and have prominent posterior tubercles.
• The foramen transversarium is small because it does not provide passage to the vertebral artery. It transmits to the accessory vertebral vein only.

Bones Of The Abdominal And Pelvic Regions

The bones of the abdominal region consist of five lumbar vertebrae and intervening intervertebral discs. The bones of the pelvic region consist of two hip bones (right and left), a sacrum, and a coccyx.

The right and left hip bones are joined anteriorly at the pubic symphysis and to the sacrum posteriorly to form a bony pelvis.

We shall first study the lumbar vertebrae, sacrum, and coccyx before studying the bony pelvis. Students are advised to review the features of a typical vertebra (as described in Chapter 4), before studying lumbar vertebrae

Lumbar Vertebrae

The lumbar region of the vertebral column consists of five lumbar vertebrae. The upper four vertebrae are typical while the fifth is atypical.

Features Of A Typical Lumbar Vertebra

Body

The bodies of lumbar vertebrae are large and kidney-shaped. The size of the lumbar vertebrae increases from above downwards as they have to bear the increasing weight of the body.

Pedicles

The pedicles are short and strong. They are directed backward and somewhat laterally. The superior vertebral notches are shallow while inferior notches are deep.

Lamina

These are broad and short and do not overlap one another as in the case of thoracic vertebrae.

Vertebral Foramen

The vertebral foramen is large and varies in shape, i.e., oval (LI) to triangular (L4).

Read and Learn More Human Osteology Notes

Transverse Processes

These are thin, long, and often have tapering ends. The posteroinferior aspect of the root of each transverse process bears a small projection called an accessory process.

Superior Articular Processes

These are vertical curved processes and bear concave articular facets facing backward and medially. There is the presence of a nonarticular rough projection on the posterior border of the superior articular process called as mammillary process.

Inferior Articular Processes

These are also vertical processes. They bear a convex articular facet, which is directed forward and laterally.

Spinous Process

The spinous process of a typical vertebra is large, thick, horizontal, and quadrilateral in shape. It presents thickened posterior and inferior borders.

Features of Fifth Lumbar Vertebra

• The fifth lumbar vertebra is the largest of all the vertebrae. The body and transverse processes of L5 are very massive as they carry the weight of the whole upper body.

• The vertical height of the anterior surface of the body is higher as compared of the posterior surface.
• This fact is responsible for a prominent sacrovertebral angle (angle between the long axis of the lumbar column and the long axis of the sacrum).
• The transverse processes of L5 are very large and thick. They have a wide origin, i.e., they arise from the lateral aspect of the pedicle and also encroach on the side of the body.
• The transverse processes of L5 are massive because they are involved in the transmission of load from the body of L5 to the ilium (through the ilio-lumbar ligament) and to the sacrum (through the lumbo-sacral ligament).
• The spinous process of the L5 vertebra is short and directed backward and somewhat downwards.
• The distance between two superior articular processes is almost equal to the distance between two inferior articular processes.
• (In the case of a typical lumbar vertebra the distance between two superior articular processes is more as compared to the distance between two inferior processes.

Clinical application

Lumbar Spinal Stenosis

• In this condition, there occurs the narrowing of the lumbar part of the vertebral canal.
• The condition may result due to bulging (prolapse) of the intervertebral disc, arthritic proliferation, or ligamentous degeneration.
• Sometimes stenosis may be congenital also. The stenosis causes compression of the spinal nerve roots of the cauda equina.
• The condition is usually treated surgically by laminectomy (excision of vertebral laminae) or by removing the entire vertebral arch.

Low Back Pain

• The neural arch at L4 and L5 levels is involved in the transmission of a considerable magnitude of load. This fact indicates that the joints between the articular facets may be the site for low back pain.
• Probably, the pain is due to stretching of the joint capsule (or transmission of load across it), which contains a nociceptive type IV receptor system (Pal and Routal, 1987).

Instability of Spine Following Laminectomy

About 20% of the load in the lumbar region passes through the laminae of lumbar vertebrae. Thus the laminectomy leads to instability of the lumbar column. Pal and Routal (1987) strongly recommended the preservation of the integrity of the articular facet joints in laminectomy.

Prolapsed or Herniated Disc

A prolapsed disc occurs when the nucleus pulposus pushes outward, distorting the shape of the disc.

If the annulus fibrosus of the disc ruptures (usually on the posterolateral aspect and most commonly at L4/L5 or L5/S1 levels) then the nucleus pulposus is herniated through the rupture.

Both in prolapsed or herniated disc surrounding tissue become inflamed and swollen. The tissue of the disc may press on the nerve or spinal cord, causing pain e.g. sciatica.

The Sacrum

The sacrum is composed of five fused sacral vertebrae in adults. It is a large, triangular wedge-shaped bone.

It is wedged between two hip bones and forms the posterior part of the bony pelvis. It transmits the weight of the upper body received through L5 to the pelvic girdle through sacroiliac joints.

The sacrum is triangular because there is a portion below the sacroiliac joint) is not involved in weight bearing hence its size diminishes rapidly.

The triangular sacrum presents an upper end or base. The base is formed by the superior surface of the SI vertebra.

It articulates with the fifth lumbar vertebra at the lumbosacral joint. The lower end of the sacrum is tapering also known as apex. It articulates with the coccyx.

The sacrum presents an anterior (or pelvic) concave surface and a dorsal (or posterior) convex surface. The pelvic surface shows the presence of four pairs of anterior sacral foramina.

Similarly, the posterior surface also shows four pairs of posterior sacral foramina the sacrum also presents the right and left lateral sacrum also presents the right and left lateral of the right and left hip bones to form sacroiliac joints The Mcra( cam, the continuation of the vertebral canal in the sacrum The canal Bes posterior to the median part of the sacrum formed by fused bodies.

The sacral canal communicates with the anterior and posterior sacral foramina through which passes the ventral and dorsal rami of sacral nerves.

Anatomical Position

Hold the bone in such a way that the pelvic (anterior) surface is directed forward and downwards. In this situation, the base of the sacrum will look forward and upwards.

General Features

The base of the Sacrum

It is formed by the upper surface of the first sacral vertebra. The base consists of a centrally placed oval body and the upper surface of the right and left ala (lateral mass) on each side of the body.

Posterior to the body there is the presence of a triangular sacral canal bounded by thick pedicles and laminae.

The superior articular facets project upwards from the junction of the pedicles and laminae.

The superior articular facets of the sacrum articulate with the inferior articular facets of the 5th lumbar vertebra.

Posteriorly, there is a resence of a tubercle at the meeting point of two laminae. This tubercle represents the rudimentary spinous process.

The body of the first sacral vertebra is large and much wider. Its anterior border is projecting and called the sacral promontory The lateral portion of the base (ala of the sacrum) is smooth and like a wing.

The ala of the sacrum is strong as it has to transmit the load from the lumbosacral joint to the sacroiliac joint.

Pelvic (Anterior) Surface

This surface is smooth, concave, and faces downwards and forwards. This surface presents four transverse lines indicating the site of fusion of 5 sacral vertebrae.

At the ends of these transverse lines, there are four pairs of sacral foramina on this surface. These foramina communicate with the sacral canal through intervertebral foramina.

Posterior (Dorsal) Surface

The dorsal surface of the sacrum is rough and convex.

• In the midline, there is the presence of a longitudinal ridge called as median sacral crest, which is formed by the fused spinous processes of the upper four sacral vertebrae The dorsal surface presents four pairs of dorsal sacral foramina, which communicate with the sacral canal and transmit dorsal rami of upper four sacral spinous nerves.
• An area between the right and left foramina is formed by the fusion of laminae of the upper four sacral vertebrae.
• The laminae Body of S1 of the fifth sacral vertebra (and sometimes the fourth also) fails to fuse in the midline and presents an inverted U or V-shaped gap called a sacral hiatus.
• On either side of the sacral hiatus are the sacral cornua, which represent the inferior articular processes of the fifth sacral vertebra.
• The sacral hiatus contains fatty connective tissue, filum-terminale, the S5 nerve and the coccygeal nerve. The sacral cornua can be easily palpated in a living person and are useful guide to locate the hiatus for the injection of anesthetic agents.
• On the medial side of dorsal sacral foramina is a vertical crest consisting of four small tubercles. These tubercles represent the fused articular processes of fused sacral vertebrae. This crest is called intermediate crest.
• On the lateral side of the dorsal sacral foramina there is the presence of lateral sacral crest. This crest is formed by the fusion of transverse processes.

Lateral Surface of the Sacrum

On both the lateral surfaces of the sacrum, there is the presence of a large ear-shaped auricular surface that articulates with the ilium of each hip bone to form a sacroiliac joint.

Posterior to the auricular surface is a rough area, the sacral tuberosity for attachment of strong interosseous sacroiliac ligament.

Apex of the Sacrum

It has an oval facet for articulation with the coccyx.

The Coccyx

It is a small triangular bone formed by the fusion of four rudimentary vertebrae. It has an upper end (base), lower end, and pelvic and dorsal surfaces.

The base is formed by the first coccygeal vertebra, which has an oval facet for articulation with the apex of the sacrum.

• The first coccygeal vertebra also has transverse processes and cornua.
• The cornua project upwards from the base of the coccyx and are connected with the cornua of the sacrum through ligaments.
• The remaining coccygeal vertebrae are featureless and represented by the nodules of bone.

Particular Features of the Sacrum and Coccyx

Attachments of the Muscles on the Sacrum and Coccyx

• lilacs and piriformis muscles are attached on the pelvic surface of the sacrum.
• The coccygeus muscle is inserted on the pelvic surface of the 5th sacral vertebra and coccyx.
• The levator ani is inserted on the tip of the coccyx.
• Note the origin of gluteus maximus from the sacrum and coccyx from their dorsal surfaces.
• The dorsal surface also gives origin to the erector spinae and multifidus.

Attachment of Ligaments

• The sacrotuberous ligament is attached to the lower part of the dorsal surface of the sacrum.
• The lateral margin of the lower part of the sacrum and the lateral margin of the coccyx gives attachment to the sacrospinous ligament.
• The interosseous ligament of the sacrospin¬ ous joint is attached to the rough area on the lateral surface posterior to the auricular surface.
• The iliolumbar ligament is attached to the lateral margin of the ala and iliac crest.
• Nerves and Blood Vessels about the Pelvic and Dorsal Surface of the Sacrum
• The median sacral artery is related to the midline.

• The lateral sacral artery is related lateral to the ventral sacral foramina.
• The right and left sympathetic trunks are related medial to the ventral sacral foramina.
• The superior rectal artery is related to the left side of the midline.
• The dorsal and ventral sacral foramina give passage to the dorsal and ventral spinal rami respectively.
• The sacral canal contains the cauda equina.
• The subdural and subarachnoid spaces end at the middle of the sacrum.
• Each ala of the sacrum is related to the following structures medial to the lateral-sympathetic trunk, lumbosacral trunk, iliolumbar artery, and obturator nerve.

Clinical Importance

Caudal Epidural Anesthesia

As the subdural and subarachnoid spaces end at the level of the middle of the sacrum, the sacral canal contains extradural or epidural space filled with fibro-fatty tissue. In this space, there are spinal nerves of cauda equina covered by dura.

In epidural anesthesia (caudal analgesia) a local anesthetic agent is injected in the sacral canal through the sacral hiatus. The sacral hiatus is located by palpating the sacral cornua and lower end of the median sacral crest.

The anesthetic agent when injected in the sacral hiatus acts on the spinal nerves in the cauda equina (usually S2 to coccygeal nerves).

This procedure is usually used to relax the perineal musculature for painless childbirth.

Abnormal Fusion of Lumbar and Sacral Vertebrae Sometimes (in about 5% of people) L5 vertebra is partly or completely fused with the sacrum.

The condition is called sacralization of the L5 vertebra. In some cases, the S1 vertebra is separated from the sacrum and may be partly or completely separated from the sacrum.

This condition is called lumbarization of the S1 vertebra. Both the above conditions may produce painful symptoms in persons having abnormal fusion of the vertebra.

Bony Pelvis

The bones of the pelvic region consist of two hip bones (right and left), a sacrum, and a coccyx. The right and left hip bones are joined anteriorly at the pubic symphysis and to the sacrum and coccyx posteriorly to form a pelvic girdle or bony pelvis.

Above it articulates with the lumbar part of the vertebral column at the lumbosacral joint. Below it is attached to the lower limbs (femora) at hip joints.

Functions of the Bony Pelvis

• The bony pelvis is the basin-shaped ring of bones, which protects the distal part of the intestine, urinary bladder, and internal genital organs.
• The main function of the bony pelvis is to transmit the weight of the upper body from the vertebral column to the lower limbs.
• It transmits the thrust between the vertebral column and lower limbs.
• Provides attachment to the powerful muscles.
• It gives passage to the fetus at the time of birth.

The bony pelvis is divided into greater and lesser pelvis. The greater pelvis is also called a false pelvis.

The lesser pelvis is called as true pelvis. The greater and lesser pelves are separated from each other by an imaginary plane, i.e., the plane of the pelvic inlet or pelvic brim).

Greater Pelvis

The walls of the greater or false pelvis are formed by the iliac fossa of the hip bones and posteriorly by the ala of the sacrum. Anteriorly, the greater pelvis presents no bony wall.

Lesser Pelvis

The lesser or true pelvis presents an inlet (superior pelvic aperture), a pelvic cavity, and an outlet (inferior pelvic aperture). The Pelvic Inlet The plane of the pelvic inlet slopes obliquely downwards and forward.

The axis of the inlet is determined by a line drawn perpendicular through the center of the plane. The plane of the pelvic inlet makes an angle of 50 to 60 with the horizontal plane.

The boundary of the pelvic inlet on each side is formed behind by the sacral promontory, the anterior margin of the ala of the sacrum, the linea terminalis, and the upper end of the symphysis pubis.

(The linea terminalis of each hip bone consists of an arcuate line of ilium iliopubic eminence, pectin pubis, and pubic crest).

The Cavity of the Lesser Pelvis

The cavity of the lesser pelvis extends downwards and backward from the pelvic inlet and lies between the inlet and outlet. Anteriorly, the cavity is bounded by the symphysis, the body of the pubis, and two rami of the pubis.

On each side, the wall is formed by ilium and ischium below the arcuate line. Posteriorly it is limited by the concave pelvic surface of the sacrum and coccyx. The posterior wall of the cavity is much longer than the anterior wall.

The Outer or Inferior Pelvic Aperture (Pelvic Outlet)

It is bounded anteriorly by the lower margin of the symphysis pubis, anterolaterally by the conjoined ischiopubic rami, laterally by the ischial tuberosities, posterolaterally by sacrotuberous ligaments, and posteriorly by the tip of the coccyx.

Thus the lower pelvic aperture is somewhat diamond-shaped. The plane of the pelvic outlet lies between the lower border of the symphysis pubis and the tip of the coccyx.

A line drawn perpendicular to the center of this plane is known axis of the pelvic outlet. The plane of the pelvic outlet makes an angle of 10 to 15 with the horizontal plane.

The Axis of Pelvic Cavity

The axis of the pelvic cavity is an imaginary axis passing through the pelvic cavity between the inlet and outlet of the pelvic cavity the axis is concave anteriorly and passes parallel to the sacrococcygeal curve.

The axis of the pelvic cavity is important because this axis passes the head of the fetus during childbirth. Hence, the axis of the pelvic cavity is also called as axis of the birth canal.

Diameters of the Pelvi

The diameter of the pelvic inlet and outlet are important in females due to childbearing

Measurements of the Inlet in Adult Females

Anteroposterior diameter: It extends between the middle of the sacral promontory to the upper margin of the symphysis pubis. It measures about 105 to 110 mm.

The transverse diameter: Is the widest measurement across the inlet. It measures about 125 to 130 mm.

The oblique diameter: It is measured from the sacroiliac joint of one side to the iliopubic eminence of the other side. It measures about 120 to 125 mm.

Measurements of the Outlets in Adult Females The anteroposterior diameter: Is measured from the lower border of the symphysis pubis to the tip of the coccyx. It is about 125 mm.

The transverse diameter: It is the distance between two ischial tuberosities. It measures about 110 to 118 mm. The oblique diameter: It is the distance between the junction of the ischiopubic ramus of one side and the midpoint of the sacrotuberous ligament of the opposite side.

Anatomical Position of the Pelvis

Hold the articulated pelvis in such a way that the upper end of the pubic symphysis and the anterior superior iliac spines lie in the same vertical plane (place these points against a wall)

In this position, the tip of the coccyx lies almost at the level of the upper margin of the symphysis pubis.

The pelvic inlet faces forward and upwards and the pelvic outlet faces downwards and backwards.

In this position sacrum faces downwards and forwards.

Differences Between Male and Female Pelves

The pelves of males and females differ significantly. These differences are due to childbearing function in females. For identification of sex from human skeletal remains, the pelvis or even a single hip bone is the most useful because here the sexual differences are clearly defined.