1 86 



THE HUMAN SPECIES 



In the membranous labyrinth of man and the domestic 

 animals there are no appreciable differences, but the organ of 

 Corti and the shape of tooth-like projections of the limbus 

 (Huschke's teeth) vary according to the species of animal. 

 In oxen and horses . . very thick. 

 cats and dogs . . pointed ends. 

 ,, rabbits . . . long and thin. 



mice .... very arched. 



man . . . height and arching little marked. 1 



Waldeyer puts the num- 

 ber of rods of Corti in man 

 at 20,000, the cords in the 

 Zona pectinata at 13,400. 



As regards the outer zone 

 of the membrane of Corti in 

 rabbits, the external margin 

 is thickest with stout glisten- 

 ing marginal fibrillae, from 

 which a fine fibrous network 

 (lamina reticularis) stretches 

 over a wide span ; in cats 

 the outer margin is fairly 

 thick, with a delicate lamina 

 reticularis, and a mere in- 

 dication of Lowenberg's 

 lamina. 



In man, on the other 

 hand, in the lowest turn 

 bounded by a marginal 

 strand there is a gradual 

 thinning of the membrane from the outer margin ; in the 

 two other turns, a free network projects terminated by fine 

 fibrillae. On the tympanic aspect of the membrane, Hensen's 

 spiral band appears as a glistening streak standing out above 

 and internal to the row of inner hair cells. - 



The appearances which are the most characteristic of the 

 human race are related to the structure of the external ear. 

 This organ, which develops as a projection from the border 

 1 Ellenberger, loc. cit., ii., p. 933. 2 Ibid., ii.. p. 938. 



FIG. 94. Human ear. a, pinna ; b, external 

 auditory meatus ; c, tympanum ; d, 

 tympanic cavity (middle ear) ; f, g, h, 

 ossicles (malleus, incus, stapes) ; i, 

 utricle; k, three semicircular canals; 

 1, sacculus ; m, cochlea ; n, auditory 

 nerve ; e, Eustachian tube. 



