Lecture 5 Skull

Objectives: learn the bones of the braincase learn the bones of the face and palate learn the cavities of the skull and associated structures

Overview: Skull The bones of the skull protect the brain and the special sense organs (sight, smell, hearing, equilibrium and taste) They form the boundaries to the entrance of the digestive and respiratory systems They also provide attachment to the facial muscles and the powerful muscles of mastication

Overview: Different breeds of dogs have different shapes and lengths of the skull. Dogs with long skulls are called dolichocephalic (e.g., Greyhound) Those with short skulls are called brachycephalic (e.g., Bulldog). The skulls of the intermediate breeds are called mesaticephalic (e.g., Dachshund).

Skull The facial bones: The braincase bones: The facial bones form the boundaries of the nasal cavity, bony orbit, and the roof and lateral walls of the oral cavity. The braincase bones: The bones of the braincase (neurocranium) form the boundaries of the cranial cavity that encloses the brain and the meninges

The bones of the braincase Neurocranium form the boundaries of the cranial cavity that encloses the brain and the meninges. The roof of the cavity (calvaria) is formed by the interparietal, parietal and frontal bones. The lateral boundaries of each side are formed by the temporal bone.

The bones of the braincase The floor is formed by the sphenoid bone and the basilar part of the occipital bone. The caudal (nuchal) wall is formed by the occipital bone and the rostral wall is formed by the ethmoid bone.

The bones of the braincase can be classified into two groups: A. Paired bones of the braincase: 1. Frontal 2. Temporal 3. Parietal   B. Unpaired bones of the braincase: 1. Interparietal 2. Occipital 3. Sphenoid 4. Ethmoid

A. Paired bones of the braincase: 1. Frontal bone: The frontal bones lie between the nasal bones and maxilla rostrally, and the parietal bones caudally. Ventrally the frontal bones articulate with sphenoid, palatine and lacrimal bones. They form the rostral part of the cranial cavity.

A. Paired bones of the braincase: The frontal bones participate in the formation of the dorsomedial part of the orbit, and envelop the ethmoid bone.

A. Paired bones of the braincase: 2. Temporal bones: The temporal bones contribute to the formation of the lower lateral wall and part of the ventral wall of the cranial cavity The temporal bone is a compound bone that is composed of three parts, squamous part, petrous part and tympanic part.

A. Paired bones of the braincase: 2. Temporal bones: The squamous part carries the zygomatic process rostrolaterally, which forms the zygomatic arch with the zygomatic process of the temporal bone. The base of the zygomatic process articulates with the condylar process of the mandible at the mandibular fossa to form the temporomandibular joint. The petrous part bears the mastoid process, which articulates with the hyoid bone. The tympanic part possesses the large tympanic bulla. The petrous and typanic parts enclose the middle and inner ear.

A. Paired bones of the braincase: 3. Parietal bone: The parietal bones are paired and they form the roof and part of the lateral sides of the cranial cavity. The parietal bones join the frontal bones rostrally and the occipital bones caudally. Ventrally the parietal bones meet the squamous temporal and basisphenoid bones

B. Unpaired bones of the braincase 1. Interparietal: The interparietal is small bone wedged in between the two parietal bones. It fuses with the occipital bone and bears the caudal part of the sagittal crest.

B. Unpaired bones of the braincase 2. Occipital: The occipital bone is formed by paired exoccipitals supraoccipital basioccipital The dorsolateral borders form the nuchal crest at the junction with the parietal and the temporal bones.

B. Unpaired bones of the braincase 2. Occipital: The external occipital protuberance is formed dorsally in the middle between the nuchal crests, where the interparietal fused with the occipital. The brain stem exists the cranial cavity through the large foramen magnum. The hypoglossal canal passes through the ventral part of the occipital bone. It provides passage for the hypoglossal nerve.

B. Unpaired bones of the braincase 3. Sphenoid: The sphenoid is formed of two bones, the rostral presphenoid and the caudal basisphenoid. The sphenoid bones form the rostral base of the braincase. Passing through the sphenoid bone are the optic canal, orbital fissure, and alar canal in the caudal part of the orbit.

B. Unpaired bones of the braincase 3. Sphenoid: The optic canal passage of the optic nerve The orbital fissure passage of oculomotor, trochlear, abducent, and ophthalmic nerves. The alar canal begins at the caudal alar foramen and ends at the rostral alar foramen. It provides a passage for the maxillary artery and nerve

B. Unpaired bones of the braincase 4. Ethmoid: The ethmoid bone is hidden between the cranial and facial parts of the skull. It consists of a median perpendicular plate a cribriform plate the ethmoidial labyrinth. consists of the ectoturbinates and endoturbinates.

Cavities of the Skull 1. Cranial Cavity 2. Nasal cavity 3. Paranasal sinuses

1. Cranial Cavity The cranial cavity contains the brain, its meninges and blood vessels. The roof of the cavity is formed by the parietal and frontal bones. The rostral wall is formed by the cribriform plate of the ethmoid The caudal wall is formed by the occipital bone. The floor or the base of the cavity is formed by the sphenoid rostrally and the temporal and occipital caudally.

2. Nasal cavity The nasal cavity begins at the bony nasal aperture and ends at the caudal openings (the choanae). It is divided into two symmetrical halves by the nasal septum. The nasal septum is composed of cartilage (septal cartilage) and bone perpendicular plate of ethmoid septal processes of frontal and nasal the sagittal portion of the vomer

2. Nasal cavity The dorsal and ventral nasal conchae divide each side of the nasal cavity into four meatuses (e.g. nasal passages). The dorsal nasal meatus lies between the dorsal concha and the nasal bone. The middle nasal meatus lies between the dorsal and ventral conchae, The ventral nasal meatus lies between the ventral concha and the floor of the nasal cavity. The previous meatuses communicate at the common nasal meatus on the sides of the nasal septum.

3. Paranasal sinuses diverticula of nasal cavity lined by nasal mucosa frontal sinus (lateral, medical, & rostral compartments) maxillary recess (sinus) — contains lateral nasal gland

3. Paranasal sinuses Frontal sinuses: There are lateral, medial and rostral frontal sinuses. The medial and the rostral frontal sinuses are small and communicate with the nasal cavity. The medial frontal sinus may be absent. The lateral frontal sinus is the largest of the three. It is bounded laterally by the temporal line and medially by the median septum.

3. Paranasal sinuses The maxillary recess : is bounded laterally and ventrally by the maxilla, and medially by the ethmoid. It opens into the nasal cavity through a transverse plane in front of the roots of the upper shearing tooth. The lateral nasal gland lies within the maxillary recess.