Overview
As in other herbivores, it is a relatively small muscle: chewing depends mainly on the masseter. In the horse the temporal fossa is wide and covers the dorsolateral surface of the cranium, between the external sagittal crest and the zygomatic arch. Rostral to it, above the eye, is the supraorbital fossa, filled with fat. The muscle passes medial to the zygomatic arch to the mandible.
Origin
Temporal fossa, bounded medially by the external sagittal crest and temporal line.
Insertion
Coronoid process of the mandible, which in the horse is tall and sits medial to the zygomatic arch.
Action
Raises the mandible and closes the mouth.
Innervation
Mandibular nerve (n. mandibularis), a branch of the trigeminal nerve (cranial nerve V).
Clinical relevance
- One-sided atrophy of the temporalis and masseter suggests a lesion of the mandibular nerve on that side.
- A sunken supraorbital fossa above the eye reflects loss of fat, not of the temporalis muscle; it is a sign of old age or poor body condition.