THE INTERNAL EAR 749 



length, and the outer rods become the longer, so that near the apex they 

 are nearly twice as long as the inner. The anatomical relations between 

 the pillars and the terminal filaments of the auditory nerves are not 

 definitely settled. 



In addition to the pillars just described, various cellular elements 

 enter into the structure of the organ of Corti. The most important of 

 these are the inner and the outer hair-cells. These are 16,400 to 20,000 

 in number (Hen sen, Waldeyer). The inner hair-cells are arranged in a 

 single row, and the outer hair-cells, in four rows. Nothing definite is 

 known of the uses of these cells. The relations of these parts are 

 shown in Fig. 196. It is supposed by some anatomists that the fila- 



* \ . 



Fig. 196. Vertical section of the organ of Corti of the dog (Waldeyer). 



a-b, homogeneous layer of the basilar membrane ; v, tympanic layer, with nuclei, granular cell- 

 protoplasm and connective tissue ; a^ tympanic lip of the crista spiralis ; c, thickened portion of the 

 basilar membrane ; d, spiral vessel ; e, bloodvessel ; / h, bundle of nerves ; g, epithelium ; i, inner 

 hair-cell, with its basilar process, k; I, head-plate of the inner pillar; m, union of the two pillars; 

 n, base of the inner pillar ; o, base of the outer pillar ; p, g, r, outer hair-cells, with traces of the cilia ; 

 /, bases of two other hair-cells ; z, Hensen's prop-cell ; /-/]_, lamina reticularis ; w, nerve-fibre passing 

 to the first hair-cell,/. 



ments of the auditory nerves terminate in the cells above described ; 

 but this point is not definitely settled. 



USES OF DIFFERENT PARTS OF THE INTERNAL EAR 



The precise uses of the different parts found in the internal ear are 

 somewhat obscure, notwithstanding the careful researches that have 

 been made into the anatomy and the physiology of the labyrinth. 

 There are several points, however, bearing on the physiology of this 

 portion of the auditory apparatus, concerning which there can be no 

 doubt : 



First, it is certain that impressions of sound are received by the 



