The structure indicated is the temporalis muscle.
This muscle is one of the muscles of mastication. The muscles of mastication include:
- Medial pterygoid
- Lateral pterygoid
The temporalis muscle is a large fan-shaped muscle which lies in the temporal fossa above the zygomatic arch.
Origin: temporal line of parietal bone. Temporal surface of sphenoid bone
Insertion: coronoid process of mandible and ramus of mandible
Innervation: mandibular branch of trigeminal nerve (cranial nerve V)
Action: Elevation of the mandible and retraction of the mandible (via posterior horizontal fibres)
To learn more about the muscles of mastication, check out this tutorial!