Difference between revisions of "Skull and Facial Muscles - Anatomy & Physiology"

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[[Image:Deer Skull with Antlers.jpg|thumb|right|150px|Deer Skull - Copyright nabrown RVC]]
  
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==Introduction==
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== Introduction ==
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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 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 [[Bone & Cartilage Development - Anatomy & Physiology|endochondral and intramembranous ossification]]. The various facial muscles attach onto the skull in different places depending on their function. Movement of the external apendages, [[Mastication|mastication]] and facial expressions all rely on the movement of the facial muscles.
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[[Image:Deer Skull with Antlers.jpg|thumb|right|200px|'''Deer Skull with Antlers''', Nabrown, date unknown]]
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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. <br> <br>  
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==Structure==
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The skull is made of many small bones, most of which are paired. Cartilage or fibrous tissue separates the bones of the skull in the young animal and once growth has ceased, the sutures begin to ossify.
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==Function==
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The skull has various functions including protection of brain, support of the facial muscles by providing origin and insertion sites, development of foramen to provide entry and exit places for the vasculature and nervous system and a defense function.
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==Bones of the Skull==
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===Occipital Bone (os occipitale)===
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[[Image:Pig skull dorsal.jpg|thumb|right|150px|Pig skull (nuchal crest, nasal bone, frontal bone, pareital bone, zygomatic process of the temporal bone and coronoid process of the mandible labelled) - Copyright nabrown RVC]]
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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 sights for muscles of the head. The '''hypoglossal canal''' is also within this structure.
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== Structure  ==
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===Sphenoid Bone (os sphenoidale)===
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[[Image:Pig skull ventral view.jpg|thumb|right|150px|Ventral view pig skull (vomer, occipital condyle, sphenoid, pterygoid bone, hamulus labelled)- Copyright nabrown RVC]]
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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 foramen (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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The skull is made of many small bones, most of which are paired. Cartilage or fibrous tissue separates the bones of the skull in the young animal and once growth has ceased, the sutures begin to ossify. <br> <br>  
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===Temporal Bone (os temporale)===
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[[Image:Zygomatic arch.jpg|thumb|right|150px|Zygomatic Arch (Dog) - Copyright nabrown RVC]]
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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, pareital 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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===Frontal Bone (os frontale)===
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The frontal bone is a paired structure joined by the '''interfrontal suture''' between the cranium and the face and enclosing the '''frontal sinuses'''. The nasal and lacrimal bones border the frontal squama section and form the zygomatic process laterally and part of the orbit dorsally. Lacrimal glands are also present near the orbit. The '''temporal line''' extends into the '''external sagittal crest'''. Ruminants also have a '''cornual process''' in [[Horn - Anatomy & Physiology|horned]] variants. The nasal section is the rostral part of the frontal bone and the orbital part is perforated by the '''ethmoidal foramen'''. Medially the '''dorsal oblique muscle''' of the eyeball attaches. The temporal part provides the muscle attachments for the '''temporalis muscle'''.
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===Parietal Bone (os parietale)===
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[[Image:Pareital Bone.jpg|thumb|right|150px|Parietal bone, occipital bone and external acoustic meatus (Horse) - Copyright nabrown RVC]]
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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 pareital 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 '''interpareital bone''' between the occipital bone and the pareital bone which fuses with age.
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== Function  ==
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===Ethmoid Bone (os ethmoidale)===
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[[Image:Nasal Cavities.jpg|thumb|right|150px|Nasal Cavities - Copyright David Bainbridge]]
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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 prodrudes 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'''
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===Nasal Bone (os nasale)===
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[[Image:Ethmoid Turbinates.jpg|thumb|right|150px|Ethmoid Turbinates (Dog) - Copyright nabrown RVC]]
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The nasal bone is a paired structure and forms the roof of the nasal cavity. '''Dorsal nasal conchae''' attach to the '''ethmoidal crest''' on the internal surface. A rostral suture forms the apex and between the nasal and incisive bones is the '''nasoincisive notch'''.
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The skull has various functions including protection of brain, support of the facial muscles by providing origin and insertion sites, development of foramen to provide entry and exit places for the vasculature and nervous system and a defense function. <br> <br>  
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===Lacrimal Bone (os lacrimale)===
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The lacrimal bone forms part of the lateral wall of the face and orbit and is situated near the '''medial canthus'''. It articulates with the '''frontal bone, zygomatic bone''' and '''maxilla'''. It also articulates with the '''nasal bone''' in ruminants and the horse and articulates with the '''palatine bone''' in carnivores. It is composed of an orbital and facial part separated by supra- and infraorbital margins. The '''nasolacrimal duct''' is present by the margin of the orbital surface. The '''ventral oblique muscle''' attaches caudal to the margin of the orbital surface. The nasal surface forms the boundaries of the '''maxillary and frontal sinuses'''.
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===Zygomatic Bone (os zygomaticum)===
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The zygomatic bone is lateral and ventral to the lacrimal bone and forms the orbit and zygomatic arch. The supraorbital margin is formed by the zygomatic process of the temporal bone and the frontal process of the zygomatic bone. The facial crest is present on lateral surface.
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===Incisive Bone (os incisivium)===
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[[Image:Cow skull lateral view.jpg|thumb|right|150px|Cow skull (incisive bone, nasal bone, maxilla, nasoincisive notch labelled) - Copyright nabrown RVC]]
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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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== Bones of the Skull  ==
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===Palatine Bone (os palatinum)===
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[[Image:Palatine Bone.jpg|thumb|right|150px|Palatine Bone and Maxilla (Pig) - Copyright nabrown RVC]]
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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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=== Occipital Bone (''os occipitale'') ===
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===Vomer===
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The vomer is unpaired and extends from the choanae of the palatine bone to the floor of the nasal cavity. It attaches to the median nuchal crest and has a '''septal sulcus''' which surrounds nasal cavity.
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===Pterygoid Bone (os pterygoideum)===
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The pterygoid bone is a paired structure bordered by the '''palatine''' and '''sphenoid bones'''. It forms the dorsal and lateral walls of the '''nasopharyngeal cavity'''. The '''pterygoid hamulus''' is formed by the pterygoid bone.
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===Maxilla===
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[[Image:Horse Maxilla.jpg|thumb|right|150px|Horse Maxilla - Copyright RVC]]
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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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===Mandible (mandibula)===
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[[Image:Cow Mandible.jpg|thumb|right|150px|Mandible of the Cow in situ - Copyright nabrown RVC]]
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[[Image:Parrot Mandible.jpg|thumb|right|150px|Mandible of the Parrot - Copyright nabrown RVC]]
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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 mandibular 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: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. <br> <br> <br>
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==Major Foramen and Canals==
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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'''.
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[[Image:Foramen Magnum.jpg|thumb|right|150px|Foramen Magnum (Horse) - Copyright nabrown RVC]]
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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]]).
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[[Image:Sheep Skull Eye Foramen.jpg|thumb|right|150px|Skull of a Sheep (optic canal, ethmoidal foramen and supraorbital foramen labelled) - Copyright nabrown RVC]]
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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'''.
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[[Image:Pig Foramen Ventral.jpg|thumb|right|150px|Foramen of the Pig (includes jugular, stylomastoid and lacernum - Copyright nabrown RVC]]
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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.
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[[Image:Cow Skull dorsal view.jpg|thumb|right|150px|Cow skull (supraorbital foramen, temporal line, supramastoid crest and supraorbital groove labelled) - Copyright nabrown RVC]]
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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'''.
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[[Image:Mental and Infraorbital Foramen.jpg|thumb|right|150px|Mental and Infraorbital foramen (dog) - Copyright nabrown RVC]]
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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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=== Sphenoid Bone (''os sphenoidale'') ===
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==Facial Muscles==
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[[Image:Muscles of Mastication.jpg|thumb|right|150px|Muscle of Mastication (dog) - Copyright C.Clarkson and T.F.Fletcher University of Minnesota]]
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The major facial muscles are covered in the following sections of anatomy and physiology:
  
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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. <br> <br> <br> <br> <br>
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[[Tongue - Anatomy & Physiology#Muscles|Muscles of the Tongue]]
  
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=== Temporal Bone (''os temporale'')  ===
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[[Cheeks|Muscles of the Cheeks]]
  
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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]]. <br> <br>
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[[Larynx - Anatomy & Physiology#Intrinsic Musculature|Muscles of the Larynx]]
  
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=== Frontal Bone (''os frontale'')  ===
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[[Pharynx - Anatomy & Physiology#Musculature|Muscles of the Pharynx]]
  
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The frontal bone is a paired structure joined by the '''interfrontal suture''' between the cranium and the face and enclosing the '''frontal sinuses'''. The nasal and lacrimal bones border the frontal squama section and form the zygomatic process laterally and part of the orbit dorsally. Lacrimal glands are also present near the orbit. The '''temporal line''' extends into the '''external sagittal crest'''. Ruminants also have a '''cornual process''' in [[Horn - Anatomy & Physiology|horned]] variants. The nasal section is the rostral part of the frontal bone and the orbital part is perforated by the '''ethmoidal foramen'''. Medially the '''dorsal oblique muscle''' of the eyeball attaches. The temporal part provides the muscle attachments for the '''temporalis muscle'''. <br> <br>
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[[Eye - Anatomy & Physiology#Around the Eye|Muscles of the Eye]]
  
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=== Parietal Bone (''os parietale'')  ===
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[[Ear - Anatomy & Physiology#Outer Ear|Muscles of the Ear]]
  
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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. <br> <br> <br> <br> <br> <br> <br>
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[[Deglutition|Muscles involved in Deglutition]]
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=== Ethmoid Bone (''os ethmoidale'')  ===
 
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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]]<br> <br> <br> <br> <br> <br> <br> <br> <br> <br>
 
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=== Nasal Bone (''os nasale'')  ===
 
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The nasal bone is a paired structure and forms the roof of the nasal cavity. '''Dorsal nasal conchae''' attach to the '''ethmoidal crest''' on the internal surface. A rostral suture forms the apex and between the nasal and incisive bones is the '''nasoincisive notch'''. <br> <br>
 
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=== Lacrimal Bone (''os lacrimale'')  ===
 
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The lacrimal bone forms part of the lateral wall of the face and orbit and is situated near the '''medial canthus'''. It articulates with the '''frontal bone, zygomatic bone''' and '''maxilla'''. It also articulates with the '''nasal bone''' in ruminants and the horse and articulates with the '''palatine bone''' in carnivores. It is composed of an orbital and facial part separated by supra- and infraorbital margins. The '''nasolacrimal duct''' is present by the margin of the orbital surface. The '''ventral oblique muscle''' attaches caudal to the margin of the orbital surface. The nasal surface forms the boundaries of the '''maxillary and frontal sinuses'''. <br> <br>
 
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−
=== Zygomatic Bone (''os zygomaticum'')  ===
 
−
 
 
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The zygomatic bone is lateral and ventral to the lacrimal bone and forms the orbit and zygomatic arch. The supraorbital margin is formed by the zygomatic process of the temporal bone and the frontal process of the zygomatic bone. The facial crest is present on lateral surface. <br> <br>
 
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−
=== Incisive Bone (''os incisivium'')  ===
 
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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. <br> <br> <br> <br> <br>
 
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−
=== Palatine Bone (''os palatinum'')  ===
 
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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. <br> <br> <br> <br> <br> <br>
 
−
 
 
−
=== Vomer  ===
 
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−
The vomer is unpaired and extends from the choanae of the palatine bone to the floor of the nasal cavity. It attaches to the median nasal crest and has a '''septal sulcus''' which surrounds nasal cavity. <br> <br>
 
−
 
 
−
=== Pterygoid Bone (''os pterygoideum'')  ===
 
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The pterygoid bone is a paired structure bordered by the '''palatine''' and '''sphenoid bones'''. It forms the dorsal and lateral walls of the '''nasopharyngeal cavity'''. The '''pterygoid hamulus''' is formed by the pterygoid bone. <br> <br>
 
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−
=== Maxilla  ===
 
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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. <br> <br>
 
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−
=== Mandible (''mandibula'')  ===
 
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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]]). <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br>
 
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−
== Major Foramen and Canals  ==
 
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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]]). <br> <br> <br> <br> <br> <br> <br> <br> [[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'''. <br> <br> <br> <br> <br> <br> [[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. <br> <br> <br> <br> <br> <br> <br> <br> <br> [[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]]). <br> <br> <br> <br> <br> <br> <br> <br> <br> <br> <br>
 
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== Facial Muscles  ==
 
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The major facial muscles are covered in the following sections of anatomy and physiology:
 
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[[Tongue - Anatomy & Physiology#Muscles|Muscles of the Tongue]]
 
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[[Cheeks|Muscles of the Cheeks]]
 
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[[Larynx - Anatomy & Physiology#Intrinsic_Musculature|Muscles of the Larynx]]
 
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[[Pharynx - Anatomy & Physiology#Musculature|Muscles of the Pharynx]]
 
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[[Eye - Anatomy & Physiology#Around_the_Eye|Muscles of the Eye]]
 
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[[Ear - Anatomy & Physiology#Outer_Ear|Muscles of the Ear]]
 
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[[Deglutition|Muscles involved in Deglutition]]  
 
  
 
[[Mastication|Muscles of Mastication]]
 
[[Mastication|Muscles of Mastication]]
  
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== Species Differences ==
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==Species Differences==
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[[Image:Pug skull.jpg|thumb|right|150px|Brachycephalic skull (Pug) - Copyright nabrown RVC]]
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=== Canine  ===
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===Canine===
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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 lacernum''' and the styloid process absent. In canines the dorsal margin of orbit 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. <br> <br> <br> <br>
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<br />
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<br />
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=== Feline  ===
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[[Image:Lion skull.jpg|thumb|right|150px|Feline skull (Lion) - Copyright nabrown RVC]]
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===Feline===
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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. <br> <br> <br>
+
The mandible appears globular in shape and the large orbits have complete bony margins. There are also large '''tympanic bulla''' 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 lacernum''' and the styloid process is absent. The dorsal margin of orbit is formed by the orbital ligament which is ossified. The '''interpareital bone''' does not fuse entirely in the adult.
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<br />
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=== Equine  ===
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<br />
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[[Image:Horse Skull.jpg|thumb|right|150px|Horse Skull - Copyright nabrown RVC]]
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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'''. <br> <br> <br> <br> <br>
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===Equine===
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+
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 pareital 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 lacernum'''. The zygomatic process articulate with the zygomatic process of the temporal bone. Horses have '''three rows of ethmoturbinates present'''.
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=== Ruminant  ===
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<br />
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<br />
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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. <br> <br> <br> <br>
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[[Image:Sheep skull.jpg|thumb|right|150px|Sheep skull - Copyright nabrown RVC]]
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===Ruminant===
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=== Porcine  ===
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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 lacernum'''. 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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<br />
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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. <br> <br> <br> <br> <br> <br>
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<br />
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[[Image:Pig skull.jpg|thumb|right|150px|Pig skull showing tusks - Copyright nabrown RVC]]
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=== Avian  ===
 
  
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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). <br> <br>
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===Porcine===
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<br>
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Pigs have a thick nucal crest and an '''internal sagittal crest''' on the internal surface of the pareital 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 absent.
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<br />
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<br />
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[[Image:Bird skull.jpg|thumb|right|150px|Bird skull - Copyright nabrown RVC]]
 +
===Avian===
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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 cartliage 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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<br />
  
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==Test yourself with our Skull and Facial Muscles Flashcards==
  
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{{Learning
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[[Skull - Musculoskeletal - Flashcards|Skull Flashcards]]
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|flashcards= [[Skull - Musculoskeletal - Flashcards|Skull]]<br>[[Facial Muscles - Musculoskeletal - Flashcards|Facial Muscles]]
 
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|videos= [[Canine Lateral Head video|Potcast of the lateral surface of the canine head]]
 
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|dragster= [[Canine Head Skeletal Anatomy Resources (I & II)]]<br>[[Canine Head Skeletal Anatomy Resources (III, IV & V)]]<br>[[Canine Facial Features Dissection Anatomy Resource]]<br>[[Canine Head Radiographical Anatomy Resources (I, II & III)]]<br>[[Canine Head Radiographical Anatomy Resources (IV & V)]]<br>[[Equine Head Dissection Anatomy Resources (I, II & III)]]<br>[[Equine Head Dissection Anatomy Resources (IV, V & VI)]]
 
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|OVAM = [http://www.onlineveterinaryanatomy.net/content/foraminae-skull-and-associated-cranial-nerves-video A short video detailing the large foraminae of the canine skull and cranial nerves associated with them.]<br>[http://www.onlineveterinaryanatomy.net/sites/default/files/original_media/document/asset_8862_REG.E.1all.pdf PDF showing a sectioned equine head with labels.]
 
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}}
 
  
 +
[[Facial Muscles - Musculoskeletal - Flashcards|Facial Muscles Flashcards]]
  
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==Webinars==
 
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<rss max="10" highlight="none">https://www.thewebinarvet.com/clinical-anatomy/webinars/feed</rss>
 
  
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[[Category:Musculoskeletal_System_-_Anatomy_&_Physiology]]
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[[Category:Musculoskeletal System - Anatomy & Physiology]]
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[[Category:Needs splitting]]
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[[Category:To Do - A&P]]

Revision as of 19:38, 23 January 2011

Deer Skull - Copyright nabrown RVC

Introduction

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, mandible, ossicles of the middle ear and the cartilage of the larynx, nose and 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 horned ungulates such as red deer stags. The neurocranium develops from the neural crest and mesoderm and undergoes 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 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 apendages, mastication and facial expressions all rely on the movement of the facial muscles.

Structure

The skull is made of many small bones, most of which are paired. Cartilage or fibrous tissue separates the bones of the skull in the young animal and once growth has ceased, the sutures begin to ossify.

Function

The skull has various functions including protection of brain, support of the facial muscles by providing origin and insertion sites, development of foramen to provide entry and exit places for the vasculature and nervous system and a defense function.

Bones of the Skull

Occipital Bone (os occipitale)

Pig skull (nuchal crest, nasal bone, frontal bone, pareital bone, zygomatic process of the temporal bone and coronoid process of the mandible labelled) - Copyright nabrown RVC

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 sights for muscles of the head. The hypoglossal canal is also within this structure.




Sphenoid Bone (os sphenoidale)

Ventral view pig skull (vomer, occipital condyle, sphenoid, pterygoid bone, hamulus labelled)- Copyright nabrown RVC

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 foramen (see species differences) including the carotid notch, oval foramen and spinous notch (in the horse). The pterygoid processes are also present.





Temporal Bone (os temporale)

Zygomatic Arch (Dog) - Copyright nabrown RVC

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, pareital 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 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 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.

Frontal Bone (os frontale)

The frontal bone is a paired structure joined by the interfrontal suture between the cranium and the face and enclosing the frontal sinuses. The nasal and lacrimal bones border the frontal squama section and form the zygomatic process laterally and part of the orbit dorsally. Lacrimal glands are also present near the orbit. The temporal line extends into the external sagittal crest. Ruminants also have a cornual process in horned variants. The nasal section is the rostral part of the frontal bone and the orbital part is perforated by the ethmoidal foramen. Medially the dorsal oblique muscle of the eyeball attaches. The temporal part provides the muscle attachments for the temporalis muscle.

Parietal Bone (os parietale)

Parietal bone, occipital bone and external acoustic meatus (Horse) - Copyright nabrown RVC

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 pareital 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 interpareital bone between the occipital bone and the pareital bone which fuses with age.







Ethmoid Bone (os ethmoidale)

Nasal Cavities - Copyright 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 (CN I) passes through. The perpendicular plate splits the ethmoid into two halves and the ethmoid larbyrinth prodrudes 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

Nasal Bone (os nasale)

Ethmoid Turbinates (Dog) - Copyright nabrown RVC

The nasal bone is a paired structure and forms the roof of the nasal cavity. Dorsal nasal conchae attach to the ethmoidal crest on the internal surface. A rostral suture forms the apex and between the nasal and incisive bones is the nasoincisive notch.







Lacrimal Bone (os lacrimale)

The lacrimal bone forms part of the lateral wall of the face and orbit and is situated near the medial canthus. It articulates with the frontal bone, zygomatic bone and maxilla. It also articulates with the nasal bone in ruminants and the horse and articulates with the palatine bone in carnivores. It is composed of an orbital and facial part separated by supra- and infraorbital margins. The nasolacrimal duct is present by the margin of the orbital surface. The ventral oblique muscle attaches caudal to the margin of the orbital surface. The nasal surface forms the boundaries of the maxillary and frontal sinuses.

Zygomatic Bone (os zygomaticum)

The zygomatic bone is lateral and ventral to the lacrimal bone and forms the orbit and zygomatic arch. The supraorbital margin is formed by the zygomatic process of the temporal bone and the frontal process of the zygomatic bone. The facial crest is present on lateral surface.

Incisive Bone (os incisivium)

Cow skull (incisive bone, nasal bone, maxilla, nasoincisive notch labelled) - Copyright nabrown RVC

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 and the opening to the nasal cavity. The alveolar process forms conical sockets for the incisor teeth.










Palatine Bone (os palatinum)

Palatine Bone and Maxilla (Pig) - Copyright nabrown RVC

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), 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

The vomer is unpaired and extends from the choanae of the palatine bone to the floor of the nasal cavity. It attaches to the median nuchal crest and has a septal sulcus which surrounds nasal cavity.

Pterygoid Bone (os pterygoideum)

The pterygoid bone is a paired structure bordered by the palatine and sphenoid bones. It forms the dorsal and lateral walls of the nasopharyngeal cavity. The pterygoid hamulus is formed by the pterygoid bone.

Maxilla

Horse Maxilla - Copyright RVC

The maxilla forms most of the facial part of the skull, including the lateral walls of the face, nasal cavity, oral cavity and 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 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)

Mandible of the Cow in situ - Copyright nabrown RVC
Mandible of the Parrot - Copyright nabrown RVC

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 mandibular 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 here).











Major Foramen and Canals

The jugular foramen is located either side of basilar part of occipital bone, adjacent to tympanic bulla and contains the glossopharyngeal nerve (CN IX), vagus nerve (CN X) and accessory nerve (CN XI). The jugular foramen also contains the internal carotid artery.

Foramen Magnum (Horse) - Copyright nabrown RVC

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 (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 (CN II).

Skull of a Sheep (optic canal, ethmoidal foramen and supraorbital foramen labelled) - Copyright nabrown RVC

The optic canal passes from the optic chiasma over wings of the presphenoid bones and facilitates the path of the optic nerve (CN II). The oval foramen is found within the caudal wing of the basisphenoid bones and the mandibular branch of the trigeminal nerve (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 (CN V2) passes through together with the temporal artery.

Foramen of the Pig (includes jugular, stylomastoid and lacernum - Copyright nabrown RVC

The stylomastoid foramen' is situated on the petrosal part of the temporal bone and allows the facial nerve (CN VII) to pass through. The ethmoidal foramen perforates the orbital part of the frontal bone allowing the olfactory nerve (CN I) and ethmoidal artery and vein to pass through.

Cow skull (supraorbital foramen, temporal line, supramastoid crest and supraorbital groove labelled) - Copyright nabrown RVC

The orbital fissure is on the presphenoid bone and allows the opthalmic branch of the trigeminal nerve (CN V1), occulomotor nerve (CN III), trochlear nerve (CN IV) and the abducens nerve (CN VI) to pass through. The supraorbital foramen is on the frontal bone and allows the opthalmic branch of the trigeminal nerve (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 (CN V2) to pass through together with the infraorbital artery and vein.

Mental and Infraorbital foramen (dog) - Copyright nabrown RVC

The mental foramen is on rostral end of the mandible and allows the mandibular branch of the trigeminal nerve (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 (CN VII). It is also the cochlear opening, dorsal vestibule opening and the ventral vestibule opening for the vestibulocochlear nerve (CN VIII).

Facial Muscles

Muscle of Mastication (dog) - Copyright C.Clarkson and T.F.Fletcher University of Minnesota

The major facial muscles are covered in the following sections of anatomy and physiology:

Muscles of the Tongue

Muscles of the Cheeks

Muscles of the Larynx

Muscles of the Pharynx

Muscles of the Eye

Muscles of the Ear

Muscles involved in Deglutition

Muscles of Mastication

Species Differences

Brachycephalic skull (Pug) - Copyright nabrown RVC

Canine

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 lacernum and the styloid process absent. In canines the dorsal margin of orbit is formed by the orbital ligament, the orbit is incomplete.

Feline skull (Lion) - Copyright nabrown RVC

Feline

The mandible appears globular in shape and the large orbits have complete bony margins. There are also large tympanic bulla 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 lacernum and the styloid process is absent. The dorsal margin of orbit is formed by the orbital ligament which is ossified. The interpareital bone does not fuse entirely in the adult.

Horse Skull - Copyright nabrown RVC

Equine

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 pareital 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 lacernum. The zygomatic process articulate with the zygomatic process of the temporal bone. Horses have three rows of ethmoturbinates present.

Sheep skull - Copyright nabrown RVC

Ruminant

In ruminants the skull is short and wide with a 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 lacernum. 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.

Pig skull showing tusks - Copyright nabrown RVC

Porcine

Pigs have a thick nucal crest and an internal sagittal crest on the internal surface of the pareital 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 absent.

Bird skull - Copyright nabrown RVC

Avian

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 cartliage 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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