THE ORGAN OF CORTI. 



661 



475. 



move Rnortened and acquire a more vertical direction, gradually passing 

 into the simple, short columnar or cubical epithelium on the outer part 

 of the basilar membrane. Between all these cells, as with those internal 

 to the inner hair-cells, is a marked amount of cuticular deposit which 

 is continuous with the outer end of the lamina reticularis (fig. i7o,p), 

 and may be looked upon as prolonging this. j\Ioreover, attached here 

 and there to the phalanges of the lamina, processes or threads of 

 cuticular substance may often be seen hanging downwards between 

 the hair-cells (fig. 470 and fig. 474, c). These 

 probably belong to certain cells which lie 

 below the hair-cells and in proximity to or 

 resting upon the basilar membrane. But the 

 exact character of the cells in this situation 

 and their relation to the hair-cells, have 

 hitherto ])afiied observation. In the guinea- 

 pig these underlying cells appear grouped, for 

 the most part, into an irregular protoplasmic 

 mass in which the rounded ends of the hair- 

 cells lie embedded, and from which curved, 

 stitf-looking processes pass in different direc- 

 tions forming a sort of supporting framework. 

 The successive series of outer hair-cells are not 

 in contact with one another (although the 

 cells of each series are so, laterally), but there 

 is a distinct interval between them filled, ap- 

 parently, only by endolymph, whicii also occu- 

 pies the meshes of the sustentacular frame- 

 work just mentioned. The whole region has 

 the appearance of l)eing kept in a state of 

 tension by means of stiff cuticular structures, 

 which serve to unite and at the same time 

 to keep apart, the reticular lamina above, and 

 the basilar membrane below. 



Fig. 475. — Four outer 

 H.iiii-CELLS IN Connec- 

 tion, WITH THEIR B.\SI- 



LAR Processes. Froji 

 theGuinea-1'ig. High- 

 ly MAGNIFIED. 



The cells belong to the 

 same series aud are viewed 

 flat. /(, one or two hair- 

 lets which have remain- 

 ed attached ; h, Inilged 

 lower end of cell ; 2)> ^^'^ 

 silar process, protoplasmic 

 above but becoming cuti- 

 cular below aud slightly 

 expanded at the extremity 

 f, which is broken away 

 from the basilar mem- 

 brane. 



than that of any other 



Considerable differences occnr in the compactness 

 with which the elements in the outer hair-cell region 

 are arranged both in different animals and in 

 different parts of the cochlea of the same animal. 

 It is in the upper turns of the cochlea that the 

 arrangement which has just been described obtains, 

 and it may be best seen in the cochlea of the guinea- 

 pig, which, indeed, for various reasons offers better 

 facilities for observation both on this and other pointi 

 animal we have examined. 



One or t^^'o peculiarities are observable in the gumea-pig's cochlea, but they do 

 not materially complicate the observation. For instance, the outer hair-cell 

 region is developed into an arching projection, the external part of the arch 

 being formed by large flattened cells, and passing abruptlj' into the low-lying 

 cubical eiiithelium of the outer part of the basilar membrane. This arched pro- 

 jection is best seen in the upper turns; and it maj- further be noticed, that in the 

 uppermost turn the flattened epithelial cells above-mentioned, possess the 

 highly-interesting peculiaritj' of con taming large fat ch-oplets so as to cause them 

 almost to appear like young fat-cells : the meaning of this development of fat is 

 entirely unknown. 



The tectorial membrane is the last special structure which remains 



