Muhammad Sohaib Shahid (Lecturer & Course Co-ordinator MID) University Institute of Radiological Sciences & Medical Imaging Technology (UIRSMIT)

BONES OF SKULL

Skull The bones of the skull can be divided into two categories, those that form the vault or cranium and enclose the brain, and those which form the framework of the face. Cranial bones There are 8 cranial bones which form a case to protect and contain the brain;

Bone No. of Bones Description Frontal bone 1 The frontal bone is a single convex bone extending from the orbits to the coronal suture behind. It forms the forehead and the roof of the orbits. Parietal bones 2 The two parietal bones form the bulk of the vault of the skull behind the frontal bone. Each bone is quadrilateral in shape and articulates with the frontal, occipital, temporal and sphenoid bones as well as with each other.   Occipital bone The occipital bone forms the back and base of the skull. It is divided into squamous, lateral and basilar parts.

Occipital bone 1 The occipital bone forms the back and base of the skull. It is divided into squamous, lateral and basilar parts. Temporal bone 2 Each temporal bone contributes to the base and to the lower lateral aspect of the skull. It is divided into squamous, petrous, mastoid and tympanic parts. The squamous part is thin, translucent and forms the anterior and upper part of the bone. The petrous part is the solid, wedge of bone that forms most of the posterior and inferior portions of the temporal bone. The mastoid part of the temporal bone lies below the squamous part and behind the tympanic part. The tympanic part of the temporal bone surrounds the external auditory meatus.

Ethmoid bone 1 The Ethmoid is a single mid line bone which forms parts of the nasal septum, medial wall of the orbital cavity and the roof and lateral wall of the nose. Sphenoid bone This single bone is found in the base of the skull and is often described as being butterfly-shaped as it consists of a central body and three paired processes.

Facial bones These 14 bones do not contribute to the cranial cavity, but form the structure of the face; Bone Number of bones Description Important Landmarks Maxilla 2 The paired maxillary bones support the teeth of the upper jaw and contribute to much of the skeleton of the upper face. Alveolar process - extends inferiorly from the body of the maxilla and supports the teeth within bony sockets. Zygomatic process - projects laterally from the body and articulates with the Zygomatic bone. Palatine process - extends horizontally to form most of the hard palate. Maxillary sinuses - are the largest of the paranasal sinuses and are situated in the bodies of the maxillary bones. It communicates with the nasal cavity through the maxillary hiatus.

Bone Number of bones Description Important Landmarks Zygomatic bones 2 The two zygomatic bones form the skeleton of the cheeks and the inferior and lateral walls of the orbit. Frontal process - forms outer margin of the orbit by articulating with the Zygomatic process of the frontal bone. Temporal process - forms the prominent Zygomatic arch by articulating with the Zygomatic process of the temporal bone. Mandible 1 The mandible is the only movable bone in the skull. It consists of a horizontal, horseshoe-shaped body and two vertical rami. Body - an arch that forms the main bulk of the mandible. Alveolar ridge - forms the superior margin of the body of the mandible and houses the lower teeth. Rami - these are the flat vertical projects that ascend from the obtuse angle of the body. Coronoid - found on the top of the ramus it lies anteriorly and serves as an attachment point for temporalis. Condylar processes - found on the top of the ramus it lies posteriorly and articulates with the temporal bone at the temporomandibular joint (TMJ).

Bone Number of bones Description Important Landmarks Palatine bones 2 The palatine bone forms part of the hard palate, the floor and lateral wall of the nasal cavity and the floor of the orbit. Horizontal plate - forms the posterior portion of the hard palate. Perpendicular plate - the medial surface forms the lateral wall of the nasal cavity and articulates with the inferior nasal concha. Orbital process - projecting from the perpendicular plate it forms the posterior part of the orbital floor. Hyoid bone 1 The horseshoe-shaped hyoid bone is situated in the upper part of the front of the neck, at the level of C3. It does not articulate with any bones but is maintained in position by the muscles, ligaments and membranes attaching to it. It gives attachment to the tongue muscles. Body - the curved medial portion of the bone. Lesser cornu - two small superior projections from the junction between the body and the greater cornu. Greater cornu - two backward projections from the body.

Lacrimal bones 2 The paired Lacrimal bones are small, thin and rectangular, and each lie in the anterior part of the medial wall of the orbit. They house the Lacrimal sac which collects tears from the eyes via the nasolacrimal duct and empties them into the nasal cavity. Lacrimal fossa - a depression that houses the Lacrimal sac. Nasal bones The two nasal bones form the upper part of the bridge of the nose. Superior border - articulates with the frontal bone. Inferior border - is continuous with the lateral nasal cartilage. Vomer 1 The vomer is a flat bone which forms the lower part of the septum of the nose. Alae - a wing like projection which articulates with the sphenoid bone. Anteriorly it articulates with the septal cartilage.