HEARING 



1069 



arranged in several rows, one row lying just internal to the inner line 

 of pillars, and several rows external to the outer line of pillars. Be- 

 tween the outer hair-cells are supporting cells (cells of Deiters). A thin 

 membrane, the reticular lamina or membrana reticularis, composed of 

 fiddle-shaped rings or phalanges, covers the hair-cells, and through 

 openings in it the hairs project. A thicker membrane, the membrana 

 tectoria, springing from the edge of the osseous spiral lamina near the 

 attachment of Reissner's membrane, forms a kind of canopy over both 

 pillars and hair-cells. The outer wall of the canal of the cochlea is 

 clad by cubical epithelium covering a membrane richly supplied with 

 bloodvessels (stria vascularis). The fact that the hair-cells of Corti's 

 organ are connected with the fibres of the cochlear division of the 



Fig. 457. Vertical Section of the First Turn of the Cochlea (after Retzius). D.C. 

 canal of cochlea; tC, tunnel of Corti; b.m, basilar membrane; h.i, h.e, internal 

 and external hair-cells; Mt, membrana tectoria; s.sp, spiral groove; str.v, stria 

 vascularis; sp.l, spiral lamina; n, fibres of the cochlear nerve; /, limbus laminae 

 spiralis; R, Reissner's membrane; s.v, scala vestibuli; s.t, scala tympani; l.sp, 

 spiral ligament. 



auditory nerve, and its elaborate structure, suggest that it must play 

 a peculiar part in auditory sensation. Comparative anatomy shows 

 us that the cochlea is the most highly developed portion of the internal 

 ear, the last to appear in its evolution, and the most specialized. It 

 is absent in fishes, which possess only a vestibule and one to three semi- 

 circular canals. It first acquires importance in reptiles, but attains 

 its highest development in mammals; and there is every reason to 

 believe that it is the terminal apparatus of the sense of hearing. 



Functions of the Auditory Ossicles. -The anatomical arrange 

 ments of the middle ear suggest that the tympanic membrane and 

 the chain of ossicles have the function of transmitting the sound- 

 waves to the liquids of the labyrinth; and observation and experi- 



