THE INTERNAL EAR. 



493 





distance is apparently straight. The head-plates of the inner pillars 

 cover the head-plates of the outer pillars (which also come in con- 

 tact with each other), also their phalangeal plates, but not their 

 phalangeal processes, which thus pro- 

 ject beyond the line formed by the 

 outer borders of the head-plates of 

 the inner pillars. It should be men- 

 tioned that about three head-plates 

 belonging to the inner pillar cells are 

 in apposition to every two head-plates 

 and their phalangeal processes of the 

 outer pillar cells. The succeeding 

 four rows, from within outward, are 

 made up of alternately placed cutic- 

 ular zones of the outer hair cells and 

 the phalangeal plates of the Deiters's 

 cells, alternating like the squares of a 

 chess-board. This regular arrange- 

 ment is lost in the outer row of 

 Deiters's cells. The cells of Hensen 

 adjoin this row, and when viewed from 

 the surface, present the appearance of 

 irregular polygons. 



This arrangement is, however, sel- 

 dom found to be as typical as that 

 just described ; although the relations 

 of the cells to one another always 

 correspond in general to the forego- 

 ing scheme. 



In the cupolar and vestibular sacs 

 the neuro-epithelium changes into an 

 epithelium of an indifferent type. 



The lamina reticularis is formed 

 by the cementing together of the pha- 

 langeal processes of the outer pillars 

 and the phalangeal plates of Deiters's 

 cells, and is continued externally by a 

 cuticular membrane which covers the 

 cells of Hensen and, as a much thin- 

 ner cuticular membrane, extends over 

 the cells of Claudius. In this mem- 

 brane there are found three or four 

 rows of small apertures, into which 

 the outer hair cells project. 



The membrana tectoria Cortii is 

 attached to the limbus spiralis, but 



becomes free at the margin of the labium vestibulare and thick- 

 ens considerably, again becoming thinner toward its free end. 



Fig. 375. Surface of the organ 

 of Corti, with the surrounding struc- 

 tures, from the basal turn of the 

 cochlea of a new-born child ; the 

 original drawing reduced one-half 

 (after Retzius, 84): a, Epithelium 

 of the sulcus spiralis externus ; b, 

 Hensen' s cells; c, terminal frame; 

 d, phalanges ; /, outer auditory cells; 

 g, flattened processes of the outer pil- 

 lar cells ; h, flattened processes of the 

 inner pillar cells ; i, inner auditory 

 cells ; k, inner sustentacular cells ; 

 /, epithelium of the sulcus spiralis 

 interims ; in, margin of the labium 

 vestibulare ; , epithelium of the 

 limbus laminae spiralis ; o, line of 

 attachment of the membrana Reiss- 

 neri ; /, epithelium of the membrana 

 Reissneri, the latter inverted. 



