MUSCULAR SYSTEM 107 
on the cranium, show great individual variation, those on the 
right sometimes differing from those on the left in one and the 
same person. By taking their physiological activities into 
account we can establish three or four stages in their 
degeneration. 
These muscles may be dealt with in four series, as under :— 
1. Muscles of the cranium, known collectively as the 
epicranius. Of this the frontal portion (frontalis) is still under 
Cy 
= 
Fic. 70.—MUSCLES OF THE EPICRANIAL REGION IN MAN, WITH CERTAIN OF THE 
FactaL Muscies. (After Gegenbaur.) 
ap., epicranial aponeurosis ; a.p., posterior auricular muscle ; @., attollens auriculam ; 
Jr., frontalis muscle ; g.p., parotid gland ; ms., masseter ; oc., m. occipitalis. 
control of the will, as is seen in frowning; but the power of 
throwing the entire epicranius into contraction, as in moving the 
scalp, is possessed by but few individuals. 
2. Muscles round the pinna: attrahens, retrahens, and 
attollens auriculam (cf. Figs. 70 and 71). The capacity for 
moving these muscles varies greatly in individuals. In most people 
it is entirely wanting; and the retrogressive character of these 
muscles is due to the degeneration of the pinna (cf. znfra). 
3. Intrinsic muscles of the pinna (derivatives of the muscles 
mentioned under 2, which have become exclusively related to the 
