Structure of the masseter muscle: - The masseter muscle is thick and quadrilateral in shape. - It consists of three heads: superficial, deep, and coronoid. - The fibers of the superficial and deep heads are continuous at their insertion. - The superficial head arises from the zygomatic process of the maxilla and the zygomatic bone. - The deep head arises from the lower border and medial surface of the zygomatic arch.

Superficial head of the masseter muscle: - The superficial head is larger than the deep head. - It arises from the zygomatic process of the maxilla and the zygomatic bone. - Its fibers pass inferior and posterior. - It is inserted into the angle of the mandible and the lateral surface of the ramus of the mandible. - The superficial head is responsible for the elevation of the mandible.

Deep head of the masseter muscle: - The deep head is smaller and more muscular in texture. - It arises from the lower border and medial surface of the zygomatic arch. - Its fibers pass downward and forward. - It is inserted into the upper half of the ramus of the mandible. - The deep head is partly concealed by the superficial portion and covered by the parotid gland.

Coronoid head of the masseter muscle: - The coronoid head of the masseter's tendon and muscle fibers run posterolaterally. - It originates from the coronoid process of the mandible. - Its function is to retract the mandible and stabilize the mandibular coronoid process. - The coronoid head plays a role in the closing of the jaws. - It is believed to contribute to the protrusion of the mandible.

Innervation of the masseter muscle: - The masseter muscle is innervated by the anterior division of the mandibular division (V3) of the trigeminal nerve. - The innervation pathway involves the gyrus precentralis, genu capsula interna, nucleus motorius nervi trigemini, nervus trigeminus, nervus mandibularis, and musculus masseter. - Along with the other muscles of mastication, the masseter receives innervation from the trigeminal nerve. - The innervation of the masseter allows for its contraction and the elevation of the mandible. - The trigeminal nerve plays a crucial role in the motor function of the masseter muscle.