422 



CHORDATE ANATOMY 



the scala tjrmpani, both of which are filled with perilymph and connected 

 with one another at the apex of the cochlea. (Fig. 371) 



The third and lower side of the cochlear duct is the essential auditory 

 organ, the spiral organ of Corti, which rests upon a connective-tissue 

 basilar membrane. In the region of the spiral organ, the epithelial lining 

 of the cochlear duct becomes a much thickened columnar epithelium, in 

 which are sensory hair-cells and supporting cells. Two kinds of support- 

 ing cells occur, pillar cells arranged like the rafters of a house, and Deiter's 



SCALA VESTIBULI 



SOUND WAVES 

 PER I LYMPH 



PILLAR CELLS 



SCALA TYMPANl 



COCHLEAR DUCT 



COCHLEAR rCRVE 



Morgan of corti '^ •«^-3^%Nv <^ - 

 Fig. 371. — A stereogram of a portion of the cochlear duct of man. The figure 

 suggests how "sound waves" are conveyed to the hair cells of the organ of Corti. 

 (Redrawn after Fritz Kahn, " Der Mensch," Albert Miiller, Zurich.) 



cells, which support the sensory hair-cells. Between them is a liquid- 

 filled cavity, the tunnel. (Fig. 370) 



The hair-cells do not extend through the entire thickness of the epithe- 

 lium, but are suspended with their rounded bases hanging between the 

 supporting cells. Four to six rows of hair-cells extend through the entire 

 length of the cochlea. An inner row is separated by the pillar cells from 

 the outer rows. 



These hair-cells are estimated to be about sixteen thousand. Each 

 has on its free surface about forty stiff hairs which project into the 



