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 



Fid. 70. MUSCLES OF THE EHICRANIAL REGION IN MAN, WITH CERTAIN OF THE 



FACIAL MUSCLES. (After Gegenbaur.) 



op., epicranial aponeurosis ; a.p. , posterior auricular muscle ; at., attollens auriculam ; 

 fr., frontalis muscle ; g.p., parotid gland ; ms., masseter ; oc., in. 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. infra}. 



3. Intrinsic muscles of the pinna (derivatives of the muscles 

 mentioned under 2, which have become exclusively related to the 



