THE MUSCLES OF THE SKIN. 95 



This muscle lies immediately beneath the integument. It 

 covers the first la}'er of body muscles. 



Action. — Moves the skin. 



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. 



(i) Most of the fibres {a) arise from the middorsal line, from 

 the occiput to the first thoracic vertebra, in a narrow ^scia 

 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 cranio- 



laterad. 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 corru- 



gator 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 



vibrissae, some to the angle of the mouth, some to the lower 



]i{). 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). 



(2) A band of fibres one or two centimeters across [a"') 

 arises in the fascia of the side of the neck just craniad of the 

 middle of the coracoid border of the scapula, and passes caudo- 



