84 THE HUMAN SPECIES 



and the non-striate, possess histological peculiarities. The striate 

 muscular fibres in man are 20^40 mm. long with an average 

 diameter of '06 mm. ; those of animals have a diameter of 

 Ooi-'Oo8 mm. 



The non-striate muscles of man are '045 - '225 long, '004 - 

 007 wide; of animals, "OO2 - '009 long, '007 -'015 wide. It 

 should further be observed that the muscles of certain mammals 

 are not uniformly red, but appear more or less pale in some 

 groups. The pale muscles exhibit distinct transverse striae but 

 almost indistinct longitudinal striae, while the red muscles 

 show exactly the opposite conditions (rabbit, guinea-pig). The 

 gradual predominance of the red over the white muscles may 

 be traced from the fishes up to the mammals. Birds may be 

 divided into graminivorous with white muscles and carnivorous 

 with red muscles. Wiedersheim, 1 who has made a special 

 study of the comparative anatomy of the muscles of man and 

 the mammals, divides the human muscles with their extraordin- 

 ary variability into three main groups : 



(1) Regressive, rudimentary. 



(2) Rare, atavistic. 



(3) Progressive. 



Among the regressive, or rudimentary, the cutaneous 

 muscles must first be mentioned, as in man and occasionally 

 also in the anthropoids only enfeebled remnants thereof 

 occur. The cutaneous muscle of the neck has shrunk into one 

 with the platysma myoides, the tendinous galea aponeurotica 

 has been developed at the cost of a part of the muse, occipitalis, 

 and of the muse, epicraneus, the muscle which moves the scalp, 

 only the m. frontalis (the corrugator of the brow) is properly 

 developed (see Fig. 37, a). In rare cases the m. epicraneus 

 persists in man together with the power of freely moving the 

 scalp up and down. 



Rudimentary also, with rare exceptions, are the muscles 

 which serve to move the external ear, the m. attrahens, m. 

 retrahens and m. attollens auriculas (see Fig. 38). The smaller 

 intrinsic muscles of the ear have entirely lost the power of 

 voluntary movement. 



The fascia axillaris may be considered as a rudiment of 

 1 Wiedersheim, loc. cit., p. 125. 



