The temporal fossa is the area on the side of the cranium from which the temporal muscle arises. The skin over this area is relatively thin and derives its blood supply from branches of the superficial temporal artery. It is drained chiefly by the superficial temporal vein. The temporal fossa is relatively flat in its superior portion and deepens inferiorly. Its lower border, which we call the infratemporal crest, is marked by several tubercles. The temporal fossa is bridged by the zygomatic arch, whose posterior (larger) root arises from the temporal squama and whose anterior root is formed by the zygomatic process of the zygoma. The temporal muscle is covered laterally by the temporal fascia, upon which course the superficial temporal vessels and the auriculotemporal nerve and its branches; these are adherent to the outer border of the zygomatic arch. From the area of the articular tubercle of the temporomandibular joint, branches of the facial nerve are distributed to the frontal belly of the epicranius muscle and to the orbicularis oculi (temporal branches of the facial nerve). The bony part of the temporal fossa is formed anteriorly by the zygomatic bone, somewhat more posteriorly by the greater wing of the sphenoid, and still farther posteriorly by the temporal squama. But the upper margin of the temporal muscle is applied to the squama of the frontal bone and to the parietal bone. Its most anterior fibers pass downward and backward at about a 10° angle (to the masticatory plane), and the adjacent fibers descend in an almost vertical line. The posterior fibers of the muscle converge forward and downward, and the most posterior fibers pass almost horizontally to their sites of attachment on the lateral and medial surfaces of the coronoid process. The deep portion of the muscle, which arises partly from the infratemporal plane of the skull, possesses a strong tendon that extends to the retromolar trigone. This tendon is easily palpated from within the oral cavity. Below the temporal fascia is the temporal aponeurosis (deep layer of the temporal fascia), which covers the temporal muscle and is attached to the medial surface of the zygomatic arch. Most of the temporal fibers arise from the temporal plane, and a few (constituting the superficial part) arise from the temporal aponeurosis. This fiber arrangement imparts a plumose structure to the muscle. A deep fiber group arises from the infratemporal plane. Most of the temporal fibers become tendinous while still above the zygomatic arch (see Fig. SA 30). The middle temporal vein, highly variable in its course and caliber, courses upon the muscle fibers which arise from this area and from the temporal aponeurosis. The temporal muscle is innervated by the anterior, middle, and posterior deep temporal nerves. These branches of the trigeminal run laterally in various directions on the infratemporal plane and pass around the infratemporal crest before entering the temporal muscle. It is believed that trauma to the nerves of the temporalis can be minimized by mobilizing the muscle from the anterior aspect. The muscle derives its blood supply from the deep temporal arteries, which spring from various branches on the external carotid and maxillary.