Ventrad of the external ear the following three differentiated portions of the platysma may be distinguished.
=M. zygomaticus= (major) (Fig. 64, _d_).--A slender band connecting the angle of the mouth with the scutiform cartilage of the ear.
[Illustration: FIG. 64.--SUPERFICIAL MUSCLES ON THE LATERAL SURFACE OF THE HEAD AND NECK.
_a_, _a′_, _a″_, M. platysma; _b_, M. depressor conchæ; _c_, M. submentalis; _d_, M. zygomaticus (_b_, _c_, and _d_ lie beneath the platysma and are seen through it); _e_, M. zygomaticus minor; _f_′, M. caninus; _f_, _g_, parts of M. quadratus labii superioris (_f_, angular head; _g_, M. levator labii superioris alæque nasi); _h_, M. myrtiformis; _i_, M. orbicularis oris; _j_, M. corrugator supercilii medialis; _k_, M. corrugator supercilii lateralis; _l_, M. adductor auris superior; _m_, M. helicis; _n_, M. antitragicus; _o_, M. adductor auris inferior; _p_, M. conchæus externus; _q_, M. abductor auris longus; _r_, parts of M. auricularis externus; _s_, M. orbicularis oculi.]
At the angle of the mouth the fibres arise from among those of the orbicularis oris (_i_), from both the upper and the lower lip. They pass thence dorsocaudad across the zygomatic arch as a band 8 or 10 millimeters wide which is attached to a tendinous aponeurosis lying just craniad of the external opening of the ear. To this aponeurosis are attached also, wholly or partly, the corrugator supercilii lateralis (_k_) and the submentalis (_c_). The aponeurosis is united with the caudoventral angle of the scutiform cartilage and with the ventral edge of the cranial margin of the auricular cartilage.
This muscle is united at its cranial end with the orbicularis oris (_i_); throughout its length more or less with the platysma (_a_, _a′_); at its caudodorsal end with the corrugator supercilii lateralis (_k_) on its medial side, and with the submentalis (_c_) on its lateral side.
_Relations._--Outer surface with the integument and the platysma (_a′_). Inner surface with the masseter, temporal, frontoscutularis, and adductor auris inferior (_o_).
_Action._--Draws the angle of the mouth dorsocaudad; the external ear ventrocraniad.
=M. submentalis= (Fig. 64, _c_).--A flat band, similar to the last, and closely connected for some distance to its caudal border.