THE COCHLEA. 607 



the thin membrane of Reissner. This space follows the turns of 

 the cochlea, lying between the vestibular coil and that leading 

 to the tympanum, and it is filled with a fluid (endolymph) which 

 is quite separate and distinct from that in the vestibular or tym- 

 panic coils of the cochlea (perilymph). 



The cochlear division of the auditory nerve passes into little 

 tunnels in the central bony column around which the coils of the 

 cochlea turn, and it gives off a spiral series of branches which 

 run through the osseous spiral lamina to reach the membranous 

 portion. A collection of ganglion cells connected with the radi- 

 ating nerve fibres is found lying in a spiral canal in the osseous 

 lamina. Passing through the bony spiral the nerves reach the 

 basilar membrane, which, as before mentioned, forms a great part 

 of the membranous spiral lamina, and upon which the organ of 

 Corti is placed. 



The organ of Corti, placed within the membranous canal of the 

 cochlea, is made up of a series of peculiarly curved bars or fibres, 

 called the rods of Corti, and some remarkable cells provided with 

 short, bristle-like processes. The rods of Corti are fixed by their 

 broad bases upon the basilar membrane, and unite above in such 

 a way that the outer and inner rods together form a bow or arch. 

 The spiral series of rods thus propped up against each other leave 

 a small space or tunnel under them, which runs the entire length 

 of the basilar membrane. Beside these rods of Corti are placed 

 rows of cells of an epithelial type into which the nerve endings 

 pass. From the upper surface of these cells, on a level with the 

 apex or junction of the rods, a number of hair-like processes pro- 

 ject. A delicate reticulated membrane lies over the rods and the 

 cells, and seems to be lightly attached to their surface, while the 

 hairs pass through its meshes. 



The basilar membrane is made up of fibrous bands held together 

 by a delicate membrane. The fibres pass transversely across the 

 spiral canal of the cochlea, so as to subtend the bases of the outer 

 and inner rods. The basilar membrane gradually becomes wider 

 as it passes from the base to the summit of the cochlea. The 

 length of the rods also increases toward the summit of the organ, 

 their bases being more widely separated from one another and 



