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== Introduction  ==

== 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. <br> <br>  

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>  

== Structure  ==

== Structure  ==

== Bones of the Skull  ==

== Bones of the Skull  ==

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

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

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

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

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

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

[[Image:Pig skull ventral view.jpg|thumb|right|150px|'''Ventral Pig Skull''', nabrown, 2008]] The sphenoid bone forms the base of the neurocranium and is composed of a body and wings. The bones are separated by cartilage which ossifies with age. The '''presphenoid (os praespenoidale)''' is rostral and has a caudal fossa which is a hollow body with sphenoid sinuses located inside. Within the sinuses are the '''optic chiasma''' and '''optic canal'''. The '''basisphenoid (os basispenoidalis)''' is caudal and has a '''median cranial fossa'''. The wings oppose the temporal bone, maxilla, orbit and the brain. The wings also form the '''oval foramen''' and other 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. <br> <br> <br> <br> <br>

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

=== Temporal Bone (os temporale)  ===

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

[[Image:Zygomatic arch.jpg|thumb|right|150px|'''Pig Zygomatic Arch''', nabrown, 2008]] The temporal bone is composed of '''squamous, petrosal''' and '''tympanic''' parts and forms the lateral wall of the cranial cavity. It articulates with the frontal, 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]]. <br> <br>

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

=== Frontal Bone (os frontale)  ===

=== Frontal Bone (os frontale)  ===