Lecture 5
Skull
Objectives:
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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
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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:
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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
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The facial bones:
• The facial bones form the boundaries of the
nasal cavity, bony orbit, and the roof and
lateral walls of the oral cavity.
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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
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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
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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
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B. Unpaired bones of the braincase:
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4.
Interparietal
Occipital
Sphenoid
Ethmoid
A. Paired bones of the braincase:
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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:
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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:
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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:
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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.
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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:
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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
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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
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2. Occipital:
The occipital bone is formed by paired
• exoccipitals
• supraoccipital
• basioccipital
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The dorsolateral borders form the
nuchal crest at the junction with the
parietal and the temporal bones.
B. Unpaired bones of the braincase
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2. Occipital:
The external occipital protuberance is
formed dorsally in the middle between the
nuchal crests, where the interparietal fused
with the occipital.
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The brain stem exists the cranial cavity
through the large foramen magnum.
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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
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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
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3. Sphenoid:
The optic canal
• passage of the optic nerve
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The orbital fissure
• passage of oculomotor, trochlear,
abducent, and ophthalmic nerves.
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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
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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.
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consists of the ectoturbinates and
endoturbinates.
Cavities of the Skull
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1. Cranial Cavity
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2. Nasal cavity
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3. Paranasal sinuses
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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.
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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
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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
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diverticula of nasal cavity lined by
nasal mucosa
frontal sinus (lateral, medical, &
rostral compartments)
maxillary recess (sinus) — contains
lateral nasal gland
3. Paranasal sinuses
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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.
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It is bounded laterally by the temporal line and
medially by the median septum.
3. Paranasal sinuses
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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.