1350 STRUCTURE OF THE COCHLEA. [BOOK m. 



the outer side, where the base of the triangle of the canalis 

 cochlearis is attached, developed into a thick cushion (Fig. 177), 

 consisting of interwoven bundles of connective tissue, among 

 which are interspersed numerous branched cells imbedded in a 

 clear matrix. Opposite the tympanic lip of the spiral lamina, 

 the bundles of fibres of this tissue converge to form a projection, 

 the spiral ligament, ligamentum spirale (Figs. 177, 179 Lg. sp.), 

 which is attached to, or rather which passes into the outer edge of 

 the basilar membrane. 



This cushion of connective tissue extends above for a short 

 distance into the region of the scala vestibuli, and for a greater 

 distance below into the region of the scala tympani; it is 

 however thickest and best developed opposite the canalis coch- 

 learis. Here it is lined by the epithelium of that canal, but 

 the characters of the epithelium in this region are somewhat 

 special. The cells are cubical or even columnar, and frequently 

 irregular in form ; they are also granular and have the aspect of 

 cells in which metabolism is active. The special characteristic 

 however is that blood vessels which are abundant in the 

 underlying connective tissue cushion traverse the line of de- 

 marcation between dermis and epithelium, and pass between 

 the epithelial cells themselves, so that, in this region, a con- 

 fusion between connective tissue and epithelial, elements takes 

 place. Owing to the peculiar prominence of the blood vessels 

 this portion of the lining of the canalis cochlearis has been 

 called the vascular band, stria vascularis (Fig. 177 Sir. v.). 

 We may probably regard it as secretory in function, analogous 

 to the choroid plexus of the brain and the ciliary processes of the 

 eye, and as taking at least a large part in furnishing the endo- 

 lymph, which it must be remembered is useful not only for 

 mechanical acoustic purposes, but also for the nourishment of the 

 delicate auditory epithelium. 



831. The remaining tympanic wall of the canalis cochlearis 

 consists, like the membrane of Reissner, of a connective tissue 

 basis with an epithelium derived from the epithelium of the otic 

 vesicle on the one side, and with lymphatic epithelioid plates on the 

 other ; but part of the epithelium, namely a portion lying midway 

 between the spiral lamina on the inside and the spiral ligament 

 on the outside, is along the whole length of the spiral, except 

 at the extreme ends, differentiated into auditory epithelium of 

 remarkable characters ; and the connective tissue basis possesses 

 corresponding special features, as indeed does also the lymphatic 

 epithelium. 



At the extreme edge of the tympanic lip of the spiral lamina 

 the ordinary bundles of fibres of connective tissue are gathered up 

 into a thin sheet which stretches radially across to the spiral 

 ligament, and there fuses again with the more ordinary con- 

 nective tissue of that ligament. It is this sheet which is called 



