372 MUSCLES. 



The Platysma Myodes, 



Or the Musculus Cutaneus, lies upon the fascia superficialis, 

 or rather is included between two laminae of it, one above and 

 the other below, forming its sheath, which is very thin, espe- 

 cially on the side next to the skin. This muscle covers, by its 

 breadth, a very considerable portion of the side of the neck; 

 and extends, obliquely, from the thorax to the face. 



It arises from the condensed cellular membrane on the upper 

 part of the pectoralis major muscle, and of the deltoid, just be- 

 low the clavicle, nearly the whole length of this bone. Its 

 fibres are much more pale than those of other voluntary mus- 

 cles, are collected into longitudinal fasciculi, constituting a 

 plane of scarcely a line in thickness, and terminate in the inte- 

 guments of the lower jaw and cheek. It is slightly attached 

 to the lower jaw, and not unfrequently runs into the muscles of 

 the lower part of the face. 



When the whole muscle is in action, it elevates the skin of 

 the neck. The external jugular vein is seen running nearly in 

 the centre of it, in the same direction with the fibres of this 

 muscle, and between it and the sterno-cleido mastoid.* 



The Sterno-Cleido Mastoideus, 



Is beneath, and decussates the last muscle. It forms always 

 a prominent feature in the outline of the neck, in passing 

 obliquely from the upper front part of the thorax to the base of 

 the cranium. 



It arises tendinous and fleshy from the edge of the upper 

 part of the sternum, and fleshy from the sternal end of the cla- 

 vicle. These origins are separated by a considerable fissure; 

 but they soon unite. It is inserted tendinous into the mastoid 

 process, and into the part of the superior transverse ridge of 

 the cranium next to it. 



It draws the chin towards the sternum. f 



* Varieties. In some rare instances this muscle has been found thick and 

 round; and instead of going towards the face, inserted into the occiput. 



t Varieties. Sometimes a fasciculus, at its posterior margin, is presented in 

 a state entirely insulated. Occasionally, its lower extremity has been observed 



