Changes

==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 - 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.

== 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 [[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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==Major Foramen and Canals==

== 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. <br> <br>

**Located either side of basilar part of occipital bone

[[Image:Foramen Magnum.jpg|thumb|right|150px|Foramen Magnum (Horse) - Copyright nabrown RVC]]

**Formed by occipital bones

**Spinal cord's passage to the neck and body

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>

**Path of the optic nerve ([[Cranial Nerves - Anatomy & Physiology|CN II]])

[[Image:Sheep Skull Eye Foramen.jpg|thumb|right|150px|Skull of a Sheep (optic canal, ethmoidal foramen and supraorbital foramen labelled) - Copyright nabrown RVC]]

**Ends from optic chiasma over wings of the presphenoid bones

== Bones of the Skull  ==

**Caudal wing of the basisphenoid bones

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

**Maxillary branch of the trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V2]])

**Facial nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]])

[[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>

[[Image:Cow Skull dorsal view.jpg|thumb|right|150px|Cow skull (supraorbital foramen, temporal line, supramastoid crest and supraorbital groove labelled) - Copyright nabrown RVC]]

**On the presphenoid bone

**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]])

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

**Opthalmic branch of the trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V1]])

[[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>

[[Image:Mental and Infraorbital Foramen.jpg|thumb|right|150px|Mental and Infraorbital foramen (dog) - Copyright nabrown RVC]]

**On rostral end of the mandible

**Mandibular branch of the trigeminal nerve ([[Cranial Nerves - Anatomy & Physiology|CN V3]])

**Mental artery and vein

[[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>

**Medial surface of the petrosal part of the temporal bone

**Facial opening for the facial nerve ([[Cranial Nerves - Anatomy & Physiology|CN VII]])

**Cochlear opening, dorsal vestibule opening and the ventral vestibule opening for the vestibulocochlear nerve ([[Cranial Nerves - Anatomy & Physiology|CN VIII]])

==Facial Muscles==

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

[[Image:Muscles of Mastication.jpg|thumb|right|150px|Muscle of Mastication (dog) - Copyright C.Clarkson and T.F.Fletcher University of Minnesota]]

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

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>

[[Larynx - Anatomy & Physiology#Intrinsic Musculature|Muscles of the Larynx]]

[[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>

[[Eye - Anatomy & Physiology#Around the Eye|Muscles of the Eye]]

[[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>

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>

[[Image:Pug skull.jpg|thumb|right|150px|Brachycephalic skull (Pug) - Copyright nabrown RVC]]

*External sagittal crest arises from nuchal crest

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>

[[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>

[[Image:Lion skull.jpg|thumb|right|150px|Feline skull (Lion) - Copyright nabrown RVC]]

*The mandible appears globular in shape

*Large tympanic bulla which can be palpated

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>

*No foramen lacernum

[[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>

*Dorsal margin of orbit formed by the orbital ligament which is ossified

[[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>

*Internal sagittal crest on the internal surface of the pareital bone

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

*Strong zygomatic arch which continues on to form the facial crest

[[Larynx - Anatomy & Physiology#Intrinsic_Musculature|Muscles of the Larynx]]

[[Mastication|Muscles of Mastication]]

 

 

 

*[[Horn - Anatomy & Physiology|Cornual]] process on frontal bone

 

 

 

 

 

 

 

*Wings of the basisphenoid bones form the oval foramen

 

 

 

[[Image:Pig skull.jpg|thumb|right|150px|Pig skull showing tusks - Copyright nabrown RVC]]

*Orbit is incomplete and small

[[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>

*Large tympanic bullae

[[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>

[[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>

[[Image:Bird skull.jpg|thumb|right|150px|Bird skull - Copyright nabrown RVC]]

*Pneumatised skull bones

**Spaces in skull bones which connect to airways in the head rather than the air sacs

*Skull plates are separated by spongy bone

[[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>

*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.

[[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>

*Middle ear contains only the columella (equivalent to the stapes)

[[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>

[[Skull - Musculoskeletal - Flashcards|Skull Flashcards]]

|flashcards= [[Skull - Musculoskeletal - Flashcards|Skull]]<br>[[Facial Muscles - Musculoskeletal - Flashcards|Facial Muscles]]

|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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