VESTIGIAL ORGANS 



muscles direct the ear as an ear-trumpet might be turned in 

 relation to a source of sound, and the muscles of the ear 

 proper change slightly the shape of that organ to adapt it 

 better, perhaps, for the reception of a given sound. The 

 human ear is incapable of these movements. The muscles, 

 though present, are ordinarily functionless, though occasion- 

 ally a person will be found who can move his ears slightly 

 and in this way demonstrate a limited control over some of 

 these muscles, but even the movement he produces is so 

 slight as to have no advantage whatever for hearing and to 

 be rather a lusus naturae than an 

 act of physiological importance. 

 In the horse and the dog the 

 movements of the ears are of 

 great value in discovering the 

 direction of sound, but the 

 muscles of the external ear of 

 man perform no work compar- 

 able to that of the ears of lower 

 animals. In man the muscles of 

 the external ear are, in the 

 strictest sense of the word, 

 vestigial. 



Not only does the ear of 

 man exhibit vestigial organs but 

 a similar organ is found in the eye. Deep-seated in the 

 nasal angle of the eye of man is a crescentic ridge of whitish 

 tissue which, in consequence of its shape, is called the plica 

 semilunaris or semilunar fold. It is not an organ that plays 

 an important part in the action of the eye; in fact, it appears 

 to be little more than a mechanical duplicature in the mem- 

 brane in adjustment to the surface which it covers, and no 

 one would suspect its meaning until he had examined the 

 eyes of lower animals. 



[41] 



1 



Fig. 6. — The human ear, 

 showing the three extrinsic 

 and four of the six intrinsic 

 vestigial muscles. 



>:\ 



Ma?^** 



