710 THE EAR 



cuticular floor for the tunnel. This uiidifferentiatcd basilar portion 

 occupies only the deeper half of the pillar cell. 



The outer hair cells form three to five rows of ciliated cells which 

 are similar in structure to the inner hair cells, and which are sup- 

 ported by the sustentacular cells of Dciters. Their cylindrical cell 

 bodies occupy the superficial third of the epithelial layer and at the 

 deeper extremity present a nucleated enlargement, beyond which they 

 are continued only as an extremely slender basal process. The free 

 ends of the outer hair cells present an expanded oval surface from which 

 the hairs project. The outer hair cells are about five times as numerous 

 as the inner, that is, there are about 3,GOO of the inner to 18,000 of 

 the outer (Waldeyer). According to certain authorities the hair cells 

 lack the delicate basal process in the adult condition. 



The outer sustentacular cells (Deiters' cells) are cylindrical cells 

 whose expanded bases rest upon the basal membrane and whose distal 

 portions extend toward the surface between the outer hair cells. The 

 superficial portion of these cells, being encroached upon by the broad 

 outer hair cells, is very slender; the broader basal portion occupies the 

 deeper two-thirds of the neuro-epithelium, the spheroidal nuclei being 

 found at the level of the middle third. Each sustentacular cell contains 

 a cuticular filament (fiber of Eetzius) which begins in contact with the 

 cuticle of the basal membrane, and extends through the axis of the 

 cell to its free border, where it expands to form a broad flattened 

 plate of peculiar shape, known as the phalangeal process. These cuticu- 

 lar processes surround and overlie the margins of the head plates of the 

 hair cells, thus forming a reticular layer through the openings of which 

 the cilia of the hair cells project. 



The cells of Deiters are succeeded by the sustentacular cells of 

 Hensen. These are tall columnar cells about eight rows broad, the inner- 

 most of which equal in height the tall cells of the preceding type, but 

 which at their outer border become abruptly shortened. Here they pass 

 into the cuboidal cells of Claudius,, and are thus continued outward to the 

 spiral ligament. 



The nuclei of the cells of Hensen are found in their superficial 

 third, those of the cells of Claudius in the center of the cell. Beneath 

 Hensen's cells other small nucleated elements are occasionally found; 

 they give to this layer somewhat the appearance of a two-rowed epi- 

 thelium and are known as the cells of Bottcher. 



Both the cells of Hensen and those of Claudius are provided with 

 a cuticular margin which, with the similar cuticle of the cells of Deiters, 



