The left side shows the first layer of muscles beneath the skin and skin-muscles; the right side shows the second layer, except in the head region. _a_, M. masseter; _b_, M. digastricus; _c_, M. mylohyoideus; _d_, M. stylohyoideus; _e_, M. sternohyoideus; _f_, M. thyreohyoideus; _g_, M. sternomastoideus; _g′_, M. sternothyreoideus; _h_, M. cleidomastoideus; _i_, M. levator scapulæ ventralis; _j_, M. clavotrapezius; _k_, M. clavobrachialis; _l_, M. pectoralis major; _m_, M. pectoantibrachialis; _n_, part of M. scalenus; _o_, M. pectoralis minor; _p_, M. xiphihumeralis; _q_, M. latissimus dorsi; _r_, M. epitrochlearis; _s_, caput longum of M. triceps brachii; _t_, M. biceps brachii; _t′_, bicipital arch; _u_, M. acromiodeltoideus; _v_, M. brachialis. 1, parotid gland; 2, submaxillary gland; 3, lymphatic glands; 4, external ear; 5, external jugular vein; 6, manubrium; 7, first rib; 8, common carotid artery; 9, molar gland.] The =deep layer= takes _Origin_ by a strong tendon from the ventral border of the zygoma just craniad of the mandibular fossa. The fibres pass cranioventrad, diverge and have their _Insertion_ into the external coronoid fossa. _Relations._--Outer surface with the following, beginning at the caudal border: the external ear, the parotid gland (Fig. 65, 1), the platysma, the submentalis, the zygomaticus (major), the zygomaticus minor. Ventral border with a lymph gland caudad of the angle of the mouth (Fig. 65, 3), and the digastric muscle (_b_). Inner surface with the bones. _Action._--A very powerful elevator of the lower jaw. =M. temporalis= (Fig. 63, _n_).--The temporal muscle is the great mass taking origin from the temporal fossa and having its insertion on both surfaces and both borders of the coronoid process of the mandible. It may be divided into two layers, deep and superficial. The =superficial layer=. The temporal fascia stretches over the temporal fossa, being attached to its borders; that is, to the sagittal and lambdoidal crests, to the curved ridge which connects the sagittal crest with the zygomatic process of the frontal bone, to the caudal border of this process, to the caudal border of the malar bone, to the caudal border of the ligament connecting the malar bone and the zygomatic process of the frontal, and to the dorsal border of the zygomatic process of the temporal bone and its dorsal root. The craniolateral part of this fascia is much stronger than the remainder. The muscle-fibres take origin from the strong craniolateral part of the inner surface of the temporal fascia, from the groove on the temporal bone dorsad of the dorsal root of its zygomatic process, from the whole inner surface of this process and of the zygomatic process of the malar bone, and sometimes also from that part of the frontal bone which lies within the temporal fossa.