g6 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 conche, 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 (1) 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 (4); 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- 
