[Illustration: FIG. 62.--MUSCLES OF THE SKIN.
_a_, _a_′, _a_″, M. platysma; _b_, M. cutaneus maximus; _c_, M. orbicularis oris. Between the platysma and the cutaneus maximus are seen the following deeper muscles: _d_, M. acromio-trapezius; _e_, M. levator scapulæ ventralis; _f_, M. spino-deltoideus; _g_, M. acromio-deltoideus; _h_, M. clavobrachialis; _i_, caput laterale of M. triceps brachii; _j_, caput longum of M. triceps brachii; _k_, M. xiphi-humeralis; _l_, M. pectoralis minor. 1, external jugular vein.]
This muscle lies immediately beneath the integument. It covers the first layer of body muscles.
=M. platysma= (Figs. 62 and 64, _a_, _a′_, _a″_).--This muscle forms a thin layer of fibres covering the sides of the neck and face, in close relation with the integument. Several more or less distinct portions may be distinguished.
(1) Most of the fibres (_a_) arise from the middorsal line, from the occiput to the first thoracic vertebra, in a narrow fascia common to the muscles of the two sides. The most cranial fibres of this region arise as a small bundle from the external occipital crest, beneath the levator auris longus (Fig. 63, _g_, _g′_).
From this origin in the middle line the fibres pass craniolaterad. The most cranial fibres curve about the ventral side of the ear and pass toward the caudal angle of the eye, where they unite with fibres of the zygomaticus (Fig. 64, _d_) or corrugator supercilii lateralis (Fig. 64, _k_), or pass to the lower eyelid. Caudad of these the fibres cover the side of the face and become lost among the facial muscles, some passing to the lower eyelid, some to the fibrous pad which supports the vibrissæ, some to the angle of the mouth, some to the lower lip. The most ventral fibres meet the fibres of the opposite muscle just ventrad of the symphysis of the mandible.
The ventral free border of the platysma is separated on the ventral side of the neck from the border of the opposite muscle by a wedge-shaped area having its point at the symphysis menti.
The fibres of this portion of the muscle are interrupted by an attachment to the skin, along a line passing from the base of the ear to about the middle of the coracoid border of the scapula, The dorsal (_a_) and ventral (_a′_) portions of the muscle, separated by this line of attachment, are sometimes described as separate muscles (the =supercervicocutaneus= and =cervicofacial=, respectively, of Strauss-Durckheim).