Skull

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Lecture

• Skull

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Overview

• 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

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Skull

• 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.
• The braincase bones
• The bones of the braincase (neurocranium) form
  the boundaries of the cranial cavity that
  encloses the brain and the meninges

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The facial bones

• The facial bones can be classified into two
  groups
• A. Paired bones of the facial bones
• 1. Lacrimal
• 2. Nasal
• 3. Maxilla
• 4. Zygomatic
• 5. Incisive
• 6. Palatine
• 7. Pterygoid
• 8. Dorsal nasal concha
• 9. Ventral nasal concha
• 10. Mandible bone
• Unpaired bones of the facial bones
• 1. Vomer
• 2. Hyoid

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A. Paired bones of the facial bones

• 1. Lacrimal
• located in the rostromedial aspect of the orbit.
• At its center there is the fossa for the lacrimal
  sac, where the osseous lacrimal canal begins.

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• The lacrimal bone articulates
• With
• frontal bone, maxilla,
• palatine bone, zygomatic bone
• and ethmoid bone.

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A. Paired bones of the facial bones

• 2. Nasal
• The nasal bone is very short in brachycephalic
  skull.
• Its internal surface is covered by mucous
  membrane in live animal.

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The nasal bone articulates with the frontal ,
maxilla and incisive bone.
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A. Paired bones of the facial bones

• 3. Maxilla
• The maxilla is the largest bone of the face.
• Together with the incisive bone, the maxilla
  forms the upper jaw.
• On its external surface there is the
  infraorbital foramen
• for the passage of infraorbital nerve, vein and
  artery.

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A. Paired bones of the facial bones

• infraorbital canal
• The canal begins at the maxillary foramen and
  ends at the infraorbital foramen.
• The short infraorbital canal lies dorsal to the
  upper fourth premolar.

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A. Paired bones of the facial bones

• 4. Zygomatic
• The zygomatic bone forms the zygomatic arch
  (rostral part) together with the zygomatic
  process of the temporal bone.
• It articulates with the maxilla, lacrimal and
  temporal bones.

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A. Paired bones of the facial bones

• 5. Incisive (Premaxilla)
• The incisive bone contains three alveoli for the
  upper incisor teeth.
• It articulates with the maxilla, vomer and nasal
  bone.

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A. Paired bones of the facial bones

• 6. Palatine
• The palatine bone forms the caudal part of the
  hard palate.
• It is divided into horizontal and perpendicular
  laminae.
• Each horizontal lamina has two surfaces, palatine
  and nasal.

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A. Paired bones of the facial bones

• 6. Palatine
• palatine canal
• Running through the palatine bone is the palatine
  canal, which provides passage for the major
  palatine artery, vein and nerve.
• The palatine canal begins at the caudal palatine
  foramen in the pterygopalatine fossa and
  terminates in the hard palate through the major
  and minor palatine foramina.

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A. Paired bones of the facial bones

• 7. Pterygoid
• The pterygoid is small four-sided bone that
  articulates with the medial surface of the
  pterygoid process of the sphenoid bone.

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A. Paired bones of the facial bones

• 8. Dorsal nasal concha
• The dorsal nasal concha is attached to the
  ethmoidal crest on the inner wall of the nasal
  bone.
• The dorsal nasal concha is a simple curved shelf
  of bone.
• The space ventral to the dorsal nasal concha is
  the middle meatus and the space dorsal to it is
  the dorsal meatus.

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A. Paired bones of the facial bones

• 9. Ventral nasal concha
• The ventral nasal concha is attached to the
  conchal crest on the medial wall of the maxilla.
• It is formed of primary and secondary bony
  scrolls.
• The space between the conchae and the nasal
  septum is the common meatus, whereas the space
  dorsal to the conchae is the middle meatus and
  the space ventral to it is the ventral meatus.

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A. Paired bones of the facial bones

• 10. Mandible
• The mandible consists of two parts that are
  united rostrally at the symphysis.
• Each part is divided into a horizontal body, and
  a vertical ramus.
• The body carries the lower teeth, and the ramus
  articulates with the temporal bone.

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A. Paired bones of the facial bones

• 10. Mandible
• The dorsal (alveolar) border of the mandible
  bears alveoli for the lower incisors, canine,
  premolars and molar teeth.
• The lateral surface of the ramus presents a
  triangular depression, the masseteric fossa, for
  the attachment of the masseter muscle.

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B. Unpaired bones of the facial bones

• 1. Vomer
• The vomer is a single bone that extends obliquely
  from the base of the cranial cavity to the upper
  surface of the hard palate.
• It forms the caudoventral part of the nasal
  septum.
• The vomer articulates with the sphenoid bone,
  ethmoid bone, palatine bones, maxilla and
  incisive bones.

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B. Unpaired bones of the facial bones

• 2. Hyoid bones
• hyoid apparatus extend from the mastoid process
  of the skull to the thyroid cartilage of the
  larynx.
• They support and stabilize the tongue and the
  larynx.

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B. Unpaired bones of the facial bones

• The hyoid apparatus consists of
• stylohyoid
• Epihyoid
• Ceratohyoid
• basihyoid
• thyrohyoid
• The basihyoid is the only single bone that
  connects the paired bones from each side at the
  root of the tongue.
• Attaching to the free end of the stylohyoid is
  the tympanohyoid cartilage, which articulates
  with the mastoid process.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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

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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.

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