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.
It arises as scattered fibres near the ventral middle line at about the level of the larynx, the fibres of the opposite muscles crossing the middle line and intermingling. The fibres pass dorsad, converging so as to form a narrower band, which unites dorsad with the zygomaticus (d), to be inserted with it into the tendinous aponeurosis above [described].
Relations.—Outer surface with the integument and platysma (a′). Inner surface with the muscles of the hyoid, the digastricus, the parotid gland, the masseter, the zygomatic arch and the temporal muscle.