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Skull and Facial Muscles - Anatomy & Physiology (view source)

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== Introduction ==

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[[Image:Deer Skull with Antlers.jpg|thumb|right|~~400px~~|'''Deer Skull with Antlers''', Nabrown, date unknown]]

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[[Image:Deer Skull with Antlers.jpg|thumb|right|200px|'''Deer Skull with Antlers''', Nabrown, date unknown]]

The shape and size of the skull varies widely, not only between species but also with age, breed and sex of similar species. The skull is divided into three components - the '''neurocranium''', the '''dermatocranium''' and the '''viscerocranium'''. The skull also includes the '''[[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]''', '''mandible''', '''ossicles of the middle [[Ear - Anatomy & Physiology|ear]]''' and the cartilage of the '''[[Larynx - Anatomy & Physiology|larynx]]''', '''nose''' and '''[[Ear - Anatomy & Physiology|ear]]'''. The skull protects the brain and head against injury and supports the structures of the face. In some animals the skull is also used for defensive actions, for example in [[Horn - Anatomy & Physiology|horned]] ungulates such as red deer stags. The '''neurocranium''' develops from the neural crest and mesoderm and undergoes [[Bone & Cartilage Development - Anatomy & Physiology|endochondral ossification]]. It lies ventral to the brain. The '''dermatocranium''' lies dorsal to the brain and develops from the neural crest and mesoderm. It undergoes [[Bone & Cartilage Development - Anatomy & Physiology#1._Intramembranous_Ossification|intramembranous ossification]]. The '''viscerocranium''' is the pharyngeal skeleton. It is derived only from the neural crest and undergoes endochondral and intramembranous ossification. The various facial muscles attach onto the skull in different places depending on their function. Movement of the external appendages, [[Mastication|mastication]] and facial expressions all rely on the movement of the facial muscles.

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=== Occipital Bone (''os occipitale'') ===

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[[Image:Pig skull dorsal.jpg|thumb|right|~~150px~~|'''Dorsal Pig skull''', nabrown, 2008]] The occipital bone forms the '''nuchal wall''' and the '''foramen magnum'''. The '''pars basilaris''' element is the caudal base of the cranium, although rostral to foramen magnum and joined by a cartilagenous suture to '''basisphenoid bone'''. It has muscular tubercules on ventral surface where the flexors of the head and neck attach and a caudocranial fossa encloses the pons and medulla oblongata. The squamous part '''''(pars squamosa)''''' is dorsal to lateral parts and occipital condyles. A nuchal crest is present and is easily palpable. The nuchal crest is often used as a landmark for collection of cerebrospinal fluid (CSF). There are also external occipital protuberances present which provide muscle attachment sites for the nuchal ligament. The lateral parts '''''(partes laterales)''''' form the borders of foramen magnum. '''Occipital condyles''' are present which articulate with the atlas to form the atlanto-occipital joint. The '''paracondylar process''' provide muscle attachment sites for muscles of the head. The '''hypoglossal canal''' is also within this structure.

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[[Image:Pig skull dorsal.jpg|thumb|right|200px|'''Dorsal Pig skull''', nabrown, 2008]] The occipital bone forms the '''nuchal wall''' and the '''foramen magnum'''. The '''pars basilaris''' element is the caudal base of the cranium, although rostral to foramen magnum and joined by a cartilagenous suture to '''basisphenoid bone'''. It has muscular tubercules on ventral surface where the flexors of the head and neck attach and a caudocranial fossa encloses the pons and medulla oblongata. The squamous part '''''(pars squamosa)''''' is dorsal to lateral parts and occipital condyles. A nuchal crest is present and is easily palpable. The nuchal crest is often used as a landmark for collection of cerebrospinal fluid (CSF). There are also external occipital protuberances present which provide muscle attachment sites for the nuchal ligament. The lateral parts '''''(partes laterales)''''' form the borders of foramen magnum. '''Occipital condyles''' are present which articulate with the atlas to form the atlanto-occipital joint. The '''paracondylar process''' provide muscle attachment sites for muscles of the head. The '''hypoglossal canal''' is also within this structure.

=== Sphenoid Bone (''os sphenoidale'') ===

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[[Image:Pig skull ventral view.jpg|thumb|right|~~150px~~|'''Ventral Pig Skull''', nabrown, 2008]] The sphenoid bone forms the base of the neurocranium and is composed of a body and wings. The bones are separated by cartilage which ossifies with age. The '''presphenoid (''os praespenoidale'')''' is rostral and has a caudal fossa which is a hollow body with sphenoid sinuses located inside. Within the sinuses are the '''optic chiasma''' and '''optic canal'''. The '''basisphenoid (''os basispenoidalis'')''' is caudal and has a '''median cranial fossa'''. The wings oppose the temporal bone, maxilla, orbit and the brain. The wings also form the '''oval foramen''' and other foramena (see [[Skull and Facial Muscles - Anatomy & Physiology#Species_Differences|species differences]]) including the '''carotid notch, oval foramen''' and '''spinous notch''' (in the horse). The pterygoid processes are also present.

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[[Image:Pig skull ventral view.jpg|thumb|right|200px|'''Ventral Pig Skull''', nabrown, 2008]] The sphenoid bone forms the base of the neurocranium and is composed of a body and wings. The bones are separated by cartilage which ossifies with age. The '''presphenoid (''os praespenoidale'')''' is rostral and has a caudal fossa which is a hollow body with sphenoid sinuses located inside. Within the sinuses are the '''optic chiasma''' and '''optic canal'''. The '''basisphenoid (''os basispenoidalis'')''' is caudal and has a '''median cranial fossa'''. The wings oppose the temporal bone, maxilla, orbit and the brain. The wings also form the '''oval foramen''' and other foramena (see [[Skull and Facial Muscles - Anatomy & Physiology#Species_Differences|species differences]]) including the '''carotid notch, oval foramen''' and '''spinous notch''' (in the horse). The pterygoid processes are also present.

=== Temporal Bone (''os temporale'') ===

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[[Image:Zygomatic arch.jpg|thumb|right|~~150px~~|'''Pig Zygomatic Arch''', nabrown, 2008]] The temporal bone is composed of '''squamous, petrosal''' and '''tympanic''' parts and forms the lateral wall of the cranial cavity. It articulates with the frontal, parietal and sphenoid bones. The squamous element joins the temporal process of the zygomatic bone to form the '''zygomatic arch''' and forms the articulating surface of the '''[[Mastication#Jaw_Articulation|temporomandibular joint]]'''. An '''articular tubercle''' and '''mandibular fossa''' are present. Occipital process and retrotympanic processes surround the '''external acoustic meatus''' whilst the petrosal part encloses the inner ear internally via the '''internal acoustic meatus'''. Ventrally this structure forms the '''mastoid process'''. The '''styloid process''' attaches the '''[[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]''' and a '''stylomastoid foramen''' is also present. The tympanic part is the ventral section of the temporal bone containing the '''tympanic bulla'''. The '''tympanic membrane''' separates tympanic cavity from '''external acoustic meatus''' and encloses the '''auditory ossicle''' dorsally. The musculotubal canal contains tensors of the [[Soft Palate#Musculature_and_Innervation|soft palate]].

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[[Image:Zygomatic arch.jpg|thumb|right|200px|'''Pig Zygomatic Arch''', nabrown, 2008]] The temporal bone is composed of '''squamous, petrosal''' and '''tympanic''' parts and forms the lateral wall of the cranial cavity. It articulates with the frontal, parietal and sphenoid bones. The squamous element joins the temporal process of the zygomatic bone to form the '''zygomatic arch''' and forms the articulating surface of the '''[[Mastication#Jaw_Articulation|temporomandibular joint]]'''. An '''articular tubercle''' and '''mandibular fossa''' are present. Occipital process and retrotympanic processes surround the '''external acoustic meatus''' whilst the petrosal part encloses the inner ear internally via the '''internal acoustic meatus'''. Ventrally this structure forms the '''mastoid process'''. The '''styloid process''' attaches the '''[[Hyoid Apparatus - Anatomy & Physiology|hyoid apparatus]]''' and a '''stylomastoid foramen''' is also present. The tympanic part is the ventral section of the temporal bone containing the '''tympanic bulla'''. The '''tympanic membrane''' separates tympanic cavity from '''external acoustic meatus''' and encloses the '''auditory ossicle''' dorsally. The musculotubal canal contains tensors of the [[Soft Palate#Musculature_and_Innervation|soft palate]].

=== Frontal Bone (''os frontale'') ===

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=== Parietal Bone (''os parietale'') ===

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[[Image:Pareital Bone.jpg|thumb|right|~~150px~~|'''Parietal Bone''', nabrown, 2008]] The parietal bone is a paired structure and forms the dorsolateral wall of the cranium with the cccipital bone caudally and the frontal bone rostrally. It is composed of a parietal plane, temporal plane and a nuchal plane (in the ox). Internally the grooves and ridges correspond with the gyri and sulci of the brain. There is also an '''interparietal bone''' between the occipital bone and the parietal bone which fuses with age.

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[[Image:Pareital Bone.jpg|thumb|right|200px|'''Parietal Bone''', nabrown, 2008]] The parietal bone is a paired structure and forms the dorsolateral wall of the cranium with the cccipital bone caudally and the frontal bone rostrally. It is composed of a parietal plane, temporal plane and a nuchal plane (in the ox). Internally the grooves and ridges correspond with the gyri and sulci of the brain. There is also an '''interparietal bone''' between the occipital bone and the parietal bone which fuses with age.

=== Ethmoid Bone (''os ethmoidale'') ===

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[[Image:Nasal Cavities.jpg|thumb|right|~~150px~~|'''Nasal Cavities''', David Bainbridge]] The ethmoid bone forms part of the cranial and facial parts of the skull and is located deep in the orbit. External lamina consist of the roof plate, floor plate and paired orbital plates. The ethmoid bone is separated from the cranial cavity by the '''cribiform plate'''. Numerous small foramina exist where the '''olfactory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN I]]) passes through. The perpendicular plate splits the ethmoid into two halves and the ethmoid larbyrinth protrudes from the ethmoid tubes. The tubes are composed of two rows of '''ethmoturbinates''' and air filled '''ethmoidal meatuses'''. Secondary ethmoturbinates may also be present. Ethmoturbinates are divided into '''endoturbinates''' and '''ectoturbinates'''. The first endoturbinate forms the dorsal nasal conchae and the second endoturbinate froms the middle nasal conchae. The endoturbinates form 3 nasal meatuses; the '''dorsal nasal meatus''', the '''middle nasal meatus''' and the '''ventral nasal meatus'''. [[Image:Ethmoid Turbinates.jpg|thumb|right|~~150px~~| '''Ethmoid Turbinates''', nabrown, 2008]]

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[[Image:Nasal Cavities.jpg|thumb|right|200px|'''Nasal Cavities''', David Bainbridge]] The ethmoid bone forms part of the cranial and facial parts of the skull and is located deep in the orbit. External lamina consist of the roof plate, floor plate and paired orbital plates. The ethmoid bone is separated from the cranial cavity by the '''cribiform plate'''. Numerous small foramina exist where the '''olfactory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN I]]) passes through. The perpendicular plate splits the ethmoid into two halves and the ethmoid larbyrinth protrudes from the ethmoid tubes. The tubes are composed of two rows of '''ethmoturbinates''' and air filled '''ethmoidal meatuses'''. Secondary ethmoturbinates may also be present. Ethmoturbinates are divided into '''endoturbinates''' and '''ectoturbinates'''. The first endoturbinate forms the dorsal nasal conchae and the second endoturbinate froms the middle nasal conchae. The endoturbinates form 3 nasal meatuses; the '''dorsal nasal meatus''', the '''middle nasal meatus''' and the '''ventral nasal meatus'''. [[Image:Ethmoid Turbinates.jpg|thumb|right|200px| '''Ethmoid Turbinates''', nabrown, 2008]]

=== Nasal Bone (''os nasale'') ===

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=== Incisive Bone (''os incisivium'') ===

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[[Image:Cow skull lateral view.jpg|thumb|right|~~150px~~|'''Cow skull lateral view''', nabrown, 2008]] The incisive bone is a paired structure composed of body, nasal, palatine and alveolar parts. It joins with the maxilla to form the '''interalveolar margin'''. It also forms the rostral part of the facial section of the skull, the roof of the '''[[Hard Palate|hard palate]]''' and the opening to the nasal cavity. The alveolar process forms conical sockets for the incisor teeth.

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[[Image:Cow skull lateral view.jpg|thumb|right|200px|'''Cow skull lateral view''', nabrown, 2008]] The incisive bone is a paired structure composed of body, nasal, palatine and alveolar parts. It joins with the maxilla to form the '''interalveolar margin'''. It also forms the rostral part of the facial section of the skull, the roof of the '''[[Hard Palate|hard palate]]''' and the opening to the nasal cavity. The alveolar process forms conical sockets for the incisor teeth.

=== Palatine Bone (''os palatinum'') ===

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[[Image:Palatine Bone.jpg|thumb|right|~~150px~~|'''Palatine Bone''', nabrown, 2008]] The palatine bone is a paired structure between the maxilla, sphenoid and pterygoid bones. It is composed of a horizontal plate (forms part of the [[Hard Palate|hard palate]]), perpendicular plate (forms the dorsal and lateral walls of the nasopharyngeal meatus) and the choanae. The '''nasal crest''' present on the horizontal plate. The '''palatine sinus''' is present on horizontal plate.

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[[Image:Palatine Bone.jpg|thumb|right|200px|'''Palatine Bone''', nabrown, 2008]] The palatine bone is a paired structure between the maxilla, sphenoid and pterygoid bones. It is composed of a horizontal plate (forms part of the [[Hard Palate|hard palate]]), perpendicular plate (forms the dorsal and lateral walls of the nasopharyngeal meatus) and the choanae. The '''nasal crest''' present on the horizontal plate. The '''palatine sinus''' is present on horizontal plate.

=== Vomer ===

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=== Maxilla ===

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[[Image:Horse Maxilla.jpg|thumb|right|~~150px~~|'''Horse Maxilla''', nabrown, 2008]] The maxilla forms most of the facial part of the skull, including the lateral walls of the face, nasal cavity, [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] and [[Hard Palate|hard palate]]. It also forms the ventral nasal conchae and articulates with all of the facial bones as it is the largest bone of the face. The maxillary body encloses the '''maxillary sinuses''' and forms the external surface of the face. It also forms the '''facial crest'''. The '''infraorbital foramen''' is palpable. The '''conchal crest''' is on nasal surface where the ventral nasal conchae attaches. The '''lacrimal canal''' opens into the '''lacrimal foramen''' on the nasal surface. The '''pterygopalatine surfaces''' are the caudal part of the maxilla which terminate in the '''maxillary tubercle''' where the '''sphenopalatine, maxillary''' and '''caudal palatine foramen''' are present. The '''alveolar processes''' present are separated by '''interalveolar septa'''. The '''palatine process''' forms the '''[[Hard Palate|hard palate]]''' with the palatine bone. The '''palatine fissure''' is formed at the articulation with the incisive bone. The nasal surface of palatine process forms the '''nasal crest''' and encloses part of the palatine sinuses. The oral surface has numerous palatine foramina present.

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[[Image:Horse Maxilla.jpg|thumb|right|200px|'''Horse Maxilla''', nabrown, 2008]] The maxilla forms most of the facial part of the skull, including the lateral walls of the face, nasal cavity, [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] and [[Hard Palate|hard palate]]. It also forms the ventral nasal conchae and articulates with all of the facial bones as it is the largest bone of the face. The maxillary body encloses the '''maxillary sinuses''' and forms the external surface of the face. It also forms the '''facial crest'''. The '''infraorbital foramen''' is palpable. The '''conchal crest''' is on nasal surface where the ventral nasal conchae attaches. The '''lacrimal canal''' opens into the '''lacrimal foramen''' on the nasal surface. The '''pterygopalatine surfaces''' are the caudal part of the maxilla which terminate in the '''maxillary tubercle''' where the '''sphenopalatine, maxillary''' and '''caudal palatine foramen''' are present. The '''alveolar processes''' present are separated by '''interalveolar septa'''. The '''palatine process''' forms the '''[[Hard Palate|hard palate]]''' with the palatine bone. The '''palatine fissure''' is formed at the articulation with the incisive bone. The nasal surface of palatine process forms the '''nasal crest''' and encloses part of the palatine sinuses. The oral surface has numerous palatine foramina present.

=== Mandible (''mandibula'') ===

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[[Image:Cow Mandible.jpg|thumb|right|~~150px~~|'''Cow Mandible''', nabrown, 2008]] [[Image:Parrot Mandible.jpg|thumb|right|~~150px~~|'''Parrot Mandible''', nabrown, 2008]] The mandible can be divided into the '''body''' and the '''ramus'''. The body of the mandible supports the incisor teeth (rostrally) and cheek teeth (caudally). The section of the body which does not support any teeth is called the '''interalveolar margin''' or '''diastema'''. The mandibule also contains the '''mandibular canal''' and the '''mental foramen'''. The '''facial notch''' is on the ventral surface where the '''parotid duct''' (in herbivores) and facial vessels run. The '''ramus''' extends from the caudal end of the body dorsally towards the zygomatic arch. The '''masseter muscle''' attaches to the lateral surface at the '''masseteric fossa'''. The '''medial pterygoid''' attaches to the medial surface at the '''pterygoid fossa'''. The angle of the mandible terminates dorsally in the '''condylar process''' and the '''coronoid process''' which are separated by the '''mandibular notch'''. The '''temporal muscle''' inserts onto the '''coronoid head'''. The condylar process articulates with the mandibular process of the skull (see [[Mastication#Jaw_Articulation|here]]).

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[[Image:Cow Mandible.jpg|thumb|right|200px|'''Cow Mandible''', nabrown, 2008]] [[Image:Parrot Mandible.jpg|thumb|right|200px|'''Parrot Mandible''', nabrown, 2008]] The mandible can be divided into the '''body''' and the '''ramus'''. The body of the mandible supports the incisor teeth (rostrally) and cheek teeth (caudally). The section of the body which does not support any teeth is called the '''interalveolar margin''' or '''diastema'''. The mandibule also contains the '''mandibular canal''' and the '''mental foramen'''. The '''facial notch''' is on the ventral surface where the '''parotid duct''' (in herbivores) and facial vessels run. The '''ramus''' extends from the caudal end of the body dorsally towards the zygomatic arch. The '''masseter muscle''' attaches to the lateral surface at the '''masseteric fossa'''. The '''medial pterygoid''' attaches to the medial surface at the '''pterygoid fossa'''. The angle of the mandible terminates dorsally in the '''condylar process''' and the '''coronoid process''' which are separated by the '''mandibular notch'''. The '''temporal muscle''' inserts onto the '''coronoid head'''. The condylar process articulates with the mandibular process of the skull (see [[Mastication#Jaw_Articulation|here]]).

== Major Foramen and Canals ==

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[[Image:Foramen Magnum.jpg|thumb|right|~~150px~~|'''Foramen Magnum''', nabrown, 2008]] The '''jugular foramen''' is located either side of basilar part of occipital bone, adjacent to tympanic bulla and contains the '''glossopharyngeal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN IX]]), '''vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]) and '''accessory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN XI]]). The jugular foramen also contains the '''internal carotid artery'''. The '''foramen magnum''' is formed by the occipital bones and is the spinal cord's passage to the neck and body. The '''alar ligaments''' run through the foramen magnum together with vertebral arteries, spinal arteries and tectoral membranes. The '''hypoglossal canal''' is between paracondylar and condylar processes on lateral part of occipital bone. The '''hypoglossal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN XII]]), '''condylar artery''' and '''condylar vein''' all pass through. The '''optic chiasma''' runs in a transverse depression behind the '''sphenoid rostrum''' on presphenoid bone and facilitates the path of the '''optic nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN II]]). [[Image:Sheep Skull Eye Foramen.jpg|thumb|right|~~150px~~|'''Skull Eye Foramen''', nabrown, 2008]] The '''optic canal''' passes from the '''optic chiasma''' over wings of the presphenoid bones and facilitates the path of the '''optic nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN II]]). The '''oval foramen''' is found within the caudal wing of the basisphenoid bones and the '''mandibular branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V3]]) passes through it. The '''alar canal''' is formed by the rostral border of the basisphenoid bone at the base of the pterygoid processes. It is composed of the '''caudal alar foramen, rostral alar foramen''' and the '''small alar foramen'''. The '''maxillary branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V2]]) passes through together with the '''temporal artery'''. [[Image:Pig Foramen Ventral.jpg|thumb|right|~~150px~~|'''Pig Ventral Skull Foramen''', nabrown, 2008]] The '''stylomastoid foramen''' is situated on the petrosal part of the temporal bone and allows the '''facial nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) to pass through. The '''ethmoidal foramen''' perforates the orbital part of the frontal bone allowing the '''olfactory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN I]]) and '''ethmoidal artery and vein''' to pass through. [[Image:Cow Skull dorsal view.jpg|thumb|right|~~150px~~|'''Cow Skull Dorsal View''', nabrown, 2008]] The '''orbital fissure''' is on the presphenoid bone and allows the '''opthalmic branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V1]]), '''occulomotor nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN III]]), '''trochlear nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN IV]]) and the '''abducens nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VI]]) to pass through. The '''supraorbital foramen''' is on the frontal bone and allows the '''opthalmic branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V1]]) to pass through together with the '''frontal artery and vein'''. The '''infraorbital foramen''' is on the maxilla and allows the '''maxillary branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V2]]) to pass through together with the '''infraorbital artery and vein'''. [[Image:Mental and Infraorbital Foramen.jpg|thumb|right|~~150px~~|'''Mental and Infraorbital Formen''', nabrown, 2008]] The '''mental foramen''' is on rostral end of the mandible and allows the '''mandibular branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V3]]) and the '''mental artery and vein''' to pass. The '''palatine canal''' runs through horizontal plate of palatine bone and allows the '''palatine artery''', '''palatine vein''' and '''palatine nerves''' to pass through. The '''internal acoustic meatus''' is made up of the medial surface of the petrosal part of the temporal bone and is the facial opening for the '''facial nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VII]]). It is also the cochlear opening, dorsal vestibule opening and the ventral vestibule opening for the '''vestibulocochlear nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]).

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[[Image:Foramen Magnum.jpg|thumb|right|200px|'''Foramen Magnum''', nabrown, 2008]] The '''jugular foramen''' is located either side of basilar part of occipital bone, adjacent to tympanic bulla and contains the '''glossopharyngeal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN IX]]), '''vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]) and '''accessory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN XI]]). The jugular foramen also contains the '''internal carotid artery'''. The '''foramen magnum''' is formed by the occipital bones and is the spinal cord's passage to the neck and body. The '''alar ligaments''' run through the foramen magnum together with vertebral arteries, spinal arteries and tectoral membranes. The '''hypoglossal canal''' is between paracondylar and condylar processes on lateral part of occipital bone. The '''hypoglossal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN XII]]), '''condylar artery''' and '''condylar vein''' all pass through. The '''optic chiasma''' runs in a transverse depression behind the '''sphenoid rostrum''' on presphenoid bone and facilitates the path of the '''optic nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN II]]). [[Image:Sheep Skull Eye Foramen.jpg|thumb|right|200px|'''Skull Eye Foramen''', nabrown, 2008]] The '''optic canal''' passes from the '''optic chiasma''' over wings of the presphenoid bones and facilitates the path of the '''optic nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN II]]). The '''oval foramen''' is found within the caudal wing of the basisphenoid bones and the '''mandibular branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V3]]) passes through it. The '''alar canal''' is formed by the rostral border of the basisphenoid bone at the base of the pterygoid processes. It is composed of the '''caudal alar foramen, rostral alar foramen''' and the '''small alar foramen'''. The '''maxillary branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V2]]) passes through together with the '''temporal artery'''. [[Image:Pig Foramen Ventral.jpg|thumb|right|200px|'''Pig Ventral Skull Foramen''', nabrown, 2008]] The '''stylomastoid foramen''' is situated on the petrosal part of the temporal bone and allows the '''facial nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VII]]) to pass through. The '''ethmoidal foramen''' perforates the orbital part of the frontal bone allowing the '''olfactory nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN I]]) and '''ethmoidal artery and vein''' to pass through. [[Image:Cow Skull dorsal view.jpg|thumb|right|200px|'''Cow Skull Dorsal View''', nabrown, 2008]] The '''orbital fissure''' is on the presphenoid bone and allows the '''opthalmic branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V1]]), '''occulomotor nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN III]]), '''trochlear nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN IV]]) and the '''abducens nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VI]]) to pass through. The '''supraorbital foramen''' is on the frontal bone and allows the '''opthalmic branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V1]]) to pass through together with the '''frontal artery and vein'''. The '''infraorbital foramen''' is on the maxilla and allows the '''maxillary branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V2]]) to pass through together with the '''infraorbital artery and vein'''. [[Image:Mental and Infraorbital Foramen.jpg|thumb|right|200px|'''Mental and Infraorbital Formen''', nabrown, 2008]] The '''mental foramen''' is on rostral end of the mandible and allows the '''mandibular branch of the trigeminal nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN V3]]) and the '''mental artery and vein''' to pass. The '''palatine canal''' runs through horizontal plate of palatine bone and allows the '''palatine artery''', '''palatine vein''' and '''palatine nerves''' to pass through. The '''internal acoustic meatus''' is made up of the medial surface of the petrosal part of the temporal bone and is the facial opening for the '''facial nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VII]]). It is also the cochlear opening, dorsal vestibule opening and the ventral vestibule opening for the '''vestibulocochlear nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN VIII]]).

== Facial Muscles ==

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[[Image:Muscles of Mastication.jpg|thumb|right|~~150px~~|'''Muscles of Mastication''', C.Clarkson and T.F.Fletcher, date unknown]] The major facial muscles are covered in the following sections of anatomy and physiology:

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[[Image:Muscles of Mastication.jpg|thumb|right|200px|'''Muscles of Mastication''', C.Clarkson and T.F.Fletcher, date unknown]] The major facial muscles are covered in the following sections of anatomy and physiology:

[[Tongue - Anatomy & Physiology#Muscles|Muscles of the Tongue]]

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=== Canine ===

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[[Image:Pug skull.jpg|thumb|right|~~150px~~|'''Brachycephalic skull''', nabrown, 2008]] Dogs have different skull lengths depending on breed. '''mesocephalic''' dogs have average conformation whilst '''dolichocephalic''' dogs have longer skull lengths and '''brachycephalic''' dogs have shorter skull lengths. The two sides of the mandible do not fuse allowing some movement in the canine jaw. The '''external sagittal crest''' arises from '''nuchal crest'''. The wings of the basisphenoid bones form the '''oval foramen, spinous foramen''' and '''carotid canal'''. Dogs have no '''foramen lacerum''' and the styloid process is absent. In canines, the dorsal orbital margin is formed by the orbital ligament, the orbit is incomplete.

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[[Image:Pug skull.jpg|thumb|right|200px|'''Brachycephalic skull''', nabrown, 2008]] Dogs have different skull lengths depending on breed. '''mesocephalic''' dogs have average conformation whilst '''dolichocephalic''' dogs have longer skull lengths and '''brachycephalic''' dogs have shorter skull lengths. The two sides of the mandible do not fuse allowing some movement in the canine jaw. The '''external sagittal crest''' arises from '''nuchal crest'''. The wings of the basisphenoid bones form the '''oval foramen, spinous foramen''' and '''carotid canal'''. Dogs have no '''foramen lacerum''' and the styloid process is absent. In canines, the dorsal orbital margin is formed by the orbital ligament, the orbit is incomplete.

=== Feline ===

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[[Image:Lion skull.jpg|thumb|right|~~150px~~|'''Lion skull''', nabrown, 2008]] The mandible appears globular in shape and the large orbits have complete bony margins. There are also large '''tympanic bullae''' which can be palpated. The two parts of the mandible do not fuse allowing some movement. Cats have a '''weak external sagittal crest''' arising from the '''nuchal crest'''. The wings of the basisphenoid bones form the '''oval foramen, spinous foramen''' and '''carotid canal'''. Cats have no '''foramen lacerum''' and the styloid process is absent. The dorsal margin of orbit is formed by the orbital ligament which is ossified. The '''interparietal bone''' does not fuse entirely in the adult.

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[[Image:Lion skull.jpg|thumb|right|200px|'''Lion skull''', nabrown, 2008]] The mandible appears globular in shape and the large orbits have complete bony margins. There are also large '''tympanic bullae''' which can be palpated. The two parts of the mandible do not fuse allowing some movement. Cats have a '''weak external sagittal crest''' arising from the '''nuchal crest'''. The wings of the basisphenoid bones form the '''oval foramen, spinous foramen''' and '''carotid canal'''. Cats have no '''foramen lacerum''' and the styloid process is absent. The dorsal margin of orbit is formed by the orbital ligament which is ossified. The '''interparietal bone''' does not fuse entirely in the adult.

=== Equine ===

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[[Image:Horse Skull.jpg|thumb|right|~~150px~~|'''Horse Skull''', nabrown, 2008]] Horses have a '''weak external sagittal crest''' arising from the '''nuchal crest'''. They also have an '''internal sagittal crest''' on the '''internal surface of the parietal bone'''. The orbit is placed more laterally with a complete bony rim and a strong '''zygomatic arch''' continues on to form the '''facial crest'''. There is a '''deep nasoincisive notch''' and a prominent '''hamular process'''. Horses have a very large mandible with a '''vascular notch''' and a high ramus. The wings of the basisphenoid bones form the '''oval foramen, spinous notch''' and '''carotid notch'''. Horses have a '''foramen lacerum'''. The zygomatic process articulate with the zygomatic process of the temporal bone. Horses have '''three rows of ethmoturbinates present'''.

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[[Image:Horse Skull.jpg|thumb|right|200px|'''Horse Skull''', nabrown, 2008]] Horses have a '''weak external sagittal crest''' arising from the '''nuchal crest'''. They also have an '''internal sagittal crest''' on the '''internal surface of the parietal bone'''. The orbit is placed more laterally with a complete bony rim and a strong '''zygomatic arch''' continues on to form the '''facial crest'''. There is a '''deep nasoincisive notch''' and a prominent '''hamular process'''. Horses have a very large mandible with a '''vascular notch''' and a high ramus. The wings of the basisphenoid bones form the '''oval foramen, spinous notch''' and '''carotid notch'''. Horses have a '''foramen lacerum'''. The zygomatic process articulate with the zygomatic process of the temporal bone. Horses have '''three rows of ethmoturbinates present'''.

=== Ruminant ===

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[[Image:Sheep skull.jpg|thumb|right|~~150px~~|'''Sheep skull''', nabrown, 2008]] In ruminants the skull is short and wide with a '''[[Horn - Anatomy & Physiology|cornual]]''' process on frontal bone. The nuchal crest is reduced to a '''nuchal line''', although there is a prominent '''temporal line'''. Ruminants have an elevated orbital ring which is complete but have no facial crest. There are prominent '''tympanic bullae''' and a '''nasoincisive notch''' present. The wings of the basisphenoid bones form the '''oval foramen'''. Ruminants have no '''foramen lacerum'''. The petrosal and tympanic parts of the temporal bone are fused to the squamous part. The zygomatic process articulates with the frontal process of the zygomatic bone.

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[[Image:Sheep skull.jpg|thumb|right|200px|'''Sheep skull''', nabrown, 2008]] In ruminants the skull is short and wide with a '''[[Horn - Anatomy & Physiology|cornual]]''' process on frontal bone. The nuchal crest is reduced to a '''nuchal line''', although there is a prominent '''temporal line'''. Ruminants have an elevated orbital ring which is complete but have no facial crest. There are prominent '''tympanic bullae''' and a '''nasoincisive notch''' present. The wings of the basisphenoid bones form the '''oval foramen'''. Ruminants have no '''foramen lacerum'''. The petrosal and tympanic parts of the temporal bone are fused to the squamous part. The zygomatic process articulates with the frontal process of the zygomatic bone.

=== Porcine ===

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[[Image:Pig skull.jpg|thumb|right|~~150px~~|'''Pig skull''', nabrown, 2008]] Pigs have a thick nuchal crest and an '''internal sagittal crest''' on the internal surface of the parietal bone. They have a prominent '''temporal line''' and their orbit is incomplete and small. There is a strong and deep zygomatic arch, large tympanic bullae and a high caudal part of the skull. The styloid process is absent.

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[[Image:Pig skull.jpg|thumb|right|200px|'''Pig skull''', nabrown, 2008]] Pigs have a thick nuchal crest and an '''internal sagittal crest''' on the internal surface of the parietal bone. They have a prominent '''temporal line''' and their orbit is incomplete and small. There is a strong and deep zygomatic arch, large tympanic bullae and a high caudal part of the skull. The styloid process is absent.

=== Avian ===

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[[Image:Bird skull.jpg|thumb|right|~~150px~~|'''Bird skull''', nabrown, 2008]] Birds have '''pneumatised skull bones''' which connect to airways in the head rather than the air sacs. They have large orbits and their skull plates are separated by spongy bone. A '''single occipital condyle''' articulates with the '''atlas''' allowing more rotation of the head. In parrots, the nasal bone and frontal bone are joined by a flexible cartilage structure allowing greater jaw opening which is called the craniofacial hinge. This allows kinesis to occur. Birds have thin '''jugal arches''' (equivalent to zygomatic arch) and the middle ear contains only the columella (equivalent to the stapes).

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[[Image:Bird skull.jpg|thumb|right|200px|'''Bird skull''', nabrown, 2008]] Birds have '''pneumatised skull bones''' which connect to airways in the head rather than the air sacs. They have large orbits and their skull plates are separated by spongy bone. A '''single occipital condyle''' articulates with the '''atlas''' allowing more rotation of the head. In parrots, the nasal bone and frontal bone are joined by a flexible cartilage structure allowing greater jaw opening which is called the craniofacial hinge. This allows kinesis to occur. Birds have thin '''jugal arches''' (equivalent to zygomatic arch) and the middle ear contains only the columella (equivalent to the stapes).

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Skull and Facial Muscles - Anatomy & Physiology (view source)

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