THE ORGANS OF SPECI.VL SENSE 587 



widely separated. There are thus formed by the pillars a series of 

 arches known as Corti's arches, enclosing a triangular canal, CorlVs 

 tunnel. This canal is filled with a gelatinous substance and crossed 

 by delicate nerve fibrils. As the outer pillar cells are the larger, 

 they are fewer in number, the estimated number in the human coch- 

 lea being forty-five hundred of the cuter cells and about six thousand 

 of the inner cells. 



(2) The hair cells or auditory cells lie on either side of the arches 

 of Corli, and are thus divided into inner hair cells and outer hair 

 cells. Both inner and outer hair cells are short, cylindrical elements 

 which do not extend to the basilar membrane. Each cell ends below 

 in a point, while from its free surface are given off a number of fine 

 stift" hairs. 



The inner hair cells lie in a single layer against the inner side of 

 the inner pillar cells, one hair cell resting upon about every two 

 pillars. 



The outer hair cells lie in three or four layers to the outer side of 

 the outer pillar cells, being separated from one another by susten- 

 tacular cells, the cells of Deiter, so that no two hair cells come in 

 contact. 



(3) Deiter 's Cells (Fig. 390). — These like the pillar cells are sus- 

 tentacular. Their bases rest upon the basilar membrane, where they 

 form a continuous layer. Toward the surface they become separated 

 from one another by the hair cells. The long slender portions of the 

 Deiter 's cells, which pass in between the hair cells, are known as pha- 

 langeal processes. Between the innermost of the outer hair cells and 

 the cuter pillar is a space known as NueVs space (Fig. 390, x). 



(4) Hensen's Cells (Fig. 390, a). — These are sustentacular cells, 

 which form about eight rows to the outer side of the outermost 

 Deiter 's ceils. These cells form the outer crest of Corti's organ and 

 consequently have a somewhat radial disposition, their free surfaces 

 being broad, their basal ends narrow. They decrease in height from 

 within outward, and at the end of Corti's organ become continuous 

 with the cells of Claudius (Fig. 390, b), the name given to the coch- 

 lear epithelium covering the basal membrane to the outer side of 

 Corti's organ. 



The phalangeal processes of the Deiter 's cells are cemented to- 

 gether and to the superficial parts of the outer pillars in such a man- 

 ner as to form a sort of cuticular membrane, the lamina reticularis, 

 through which the heads of the outer hair cells project. This mem- 



