394 NORMAL HISTOLOGY. 



Immediately within the arch of Corti, resting upon the inner 

 rods, a single row of specialized epithelial elements extends as 

 the inner hair-cells. These elements, little more than half the 

 thickness of the epithelial layer in length, possess a columnar body, 

 whose dark granular protoplasm contains an oval nucleus ; the 

 outer somewhat constricted end of the cells is limited by a sharply- 

 defined cuticular zone, from the free surface of which project, in 

 man, some twenty fine rods or " hairs." The inner hair-cells are 

 less numerous, as well as shorter and broader, than the correspond- 

 ing outer elements ; their numerical relation to the inner rods 

 of Corti is such that to every three rods two hair-cells are applied. 



The inner sustentacular cells extend throughout the thickness 

 of the epithelial layer, and exhibit a slightly-imbricated arrangement 

 as they pass over the sides of Corti' s organ to become continuous 

 with the lower cells of the sulcus spiralis. 



The cells covering the basilar membrane from the outer pil- 

 lar to the basilar crest comprise three groups : those composing the 

 outer part of Corti' s organ, including the outer hair-cells and cells 

 of Deiters, the outer supporting cells, or cells of Hensen, 

 and the low cuboidal elements, the cells of Claudius, investing the 

 outermost part of the basilar membrane. 



The outer hair-cells are far more numerous than the corre- 

 sponding inner elements, and in man and apes are disposed in three 

 or four rows, alternating with the peculiar end-plates or "pha- 

 langes" of Deiters's cells which separate the ends of the hair-cells 

 and join to form a cuticular net-work, the membrana reticularis, 

 through the openings of which the hair-cells reach the free surface. 

 The inner row of these cells lies directly upon the outer rods of 

 Corti, so placed that each cell, as a rule, rests upon two rods ; the 

 cells of the second row, however, are so disposed that each cell lies 

 opposite a single rod, while the third layer repeats the arrangement 

 of the first ; in consequence of this grouping these elements, in con- 

 nection with the ' ' phalanges," appear in surface views like a checker- 

 board mosaic, in which the oval free ends of the auditory cells 

 are included between the peculiar compressed and indented octag- 

 onal areas of the end-plates of Deiters's cells. 



The outer auditory or hair cells are cylindrical in their general 

 form, terminating about the middle of the epithelial layer in slightly- 

 expanded rounded ends near which the spherical nuclei are 

 situated. The outer sharply-defined ends of the cells are distin- 

 guished by a cuticular border supporting about twenty fine, rigid 

 auditory rods or " hairs" which project beyond the level of the 

 membrana reticularis. 



The sustentacular elements, the cells of Deiters, have much 



