96 THE MUSCLES. 



ventrad toward the manubrium, its fibres crossing the fibres of 

 the first part of the platysma at right angles. These fibres 

 become lost in the fascia ventrad of the manubrium, or pass 

 across the middle line to intermingle with the corresponding 

 fibres of the opposite side. This portion of the platysma is 

 sometimes absent. 



The platysma is everywhere subcutaneous, except at its 

 dorsocranial angle, where a small bundle of fibres is covered 

 by the levator longus auris. It covers the deeper muscles of 

 the neck and head. Closely attached to its inner surface- are 

 the submentalis and depressor conchae, whose fibres bridge 

 over the ventral interval between the borders of the platysmas 

 of opposite sides. 



Action. Moves the skin of the face and neck. 



II. THE MUSCLES OF THE HEAD. 



A. SUPERFICIAL MUSCLES. The most superficial layer 

 of muscles on the face and head is formed by differentiation of 

 the fibres of the platysma. The muscles thus formed are not 

 clearly distinct from each other; in this region sets of fibres 

 differing in direction and in origin or insertion receive separate 

 names even though the different sets of fibres are closely inter- 

 woven. 



In the quadrangle on the dorsal surface of the head enclosed 

 between the two eyes and the two ears, a thin superficial sheet 

 of fibres is found, in which a number of different sets may be 

 distinguished (Fig. 63). These have received the following 

 names. 



M. intermedius scutulorum (Fig. 63, a). This consists 

 of a broad thin sheet of transverse fibres between the two 

 external ears. The fibres are attached at either end to the 

 scutiform cartilage (i) of the two ears, and pass without inter- 

 ruption across the middle line. At its cranial edge this muscle 

 is continuous with the corrugator supercilii medialis (b} ; at its 

 lateral edge with the frontoscutularis ; at its caudal edge with 

 the levator auris longus (g). 



Relations. Outer surface with, the integument. Inner sur- 



