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*Digastricus muscle
*Digastricus muscle
**Origin: paracondylar process of occipital bone
**Insertion: angle of mandible
**Two bellies:
***Caudal half from the second visceral arch innervated by facial nerve (CN VII)
***Cranial half from the first visceral arch innervated by the mandibular branch of the trigeminal (CN V3)
'''Jaw Closing Muscles'''
'''Jaw Closing Muscles'''
*Masseter muscle
*Masseter muscle
**Origin: maxilliary region of skull and zygomatic arch
**Insertion: wide area on caudal side of mandible
**Several divisions
**Unilateral and bilateral contraction
**Also protrudes jaw
*Lateral Pterygoid muscle
*Lateral Pterygoid muscle
**Origin: pterygopalatine region of skull
**Insertion: lateral aspect of mandible
**Also protrudes jaw (one-sided contraction)
*Medial Pterygoid muscle
*Medial Pterygoid muscle
**Origin: pterygopalatine region of skull
**Insertion: medial aspect of mandible
**One-sided contraction to close jaw
*Temporal muscle
*Temporal muscle
**Origin: lateral surface of cranium
**Insertion: coronoid process
**Pulls mandible dorsally
**Also pulls mandible rostrally (overbite) and caudally (underbite)
'''Lateral Translation of Mandible'''
'''Lateral Translation of Mandible'''
==Species Differences==
==Species Differences==
*Large masseter and pterygoid muscles in the horse for extensive chewing
===Hebivores===
*Large masseter and pterygoid muscles for extensive chewing
*Large temporalis muscle in the carnivores for snapping the jaw shut, e.g. in lions and pitbull terriers
*Herbiverous species have a limited digastricus muscle
*In the horse the muscle insertion site for the masseter is large to snap jaw shut
*Herbiverous species have a limited digastricus muscle
===Carnivores===
*Large temporalis muscle for snapping the jaw shut, e.g. in lions and pitbull terriers
*Canids have a larger digasticus muscle than herbivores (but smaller in comparison with jaw closing muscles)
*Canids have a larger digasticus muscle than herbivores (but smaller in comparison with jaw closing muscles)
*In the dog large forces are needed to shut jaws so the point of articulation of the temporomandibular joint is level with the teeth
*In the dog large forces are needed to shut jaws so the point of articulation of the temporomandibular joint is level with the teeth