220 STRUCTURE OF THE COCHLEA. [Boon in. 



resemble those of a ganglion on the posterior root of a spinal 

 nerve ( 97); the nerve fibres are however not connected with 

 the cells by T pit-res, since the cells are typically bipolar, the 

 fibre entering the cell at one pole and issuing at the opposite 

 pole. The issuing fibre as well as the entering fibre is medullated. 



The fibres, issuing from the ganglion in bundles, break up into 

 a loose plexus, and ascend obliquely towards the tympanic lip. 

 As they approach the membranous, connective tissue end of the 

 lip, the fibres are gathered into aseries of more close set plexuses, 

 which pierce the lip through a series of slit-like orifices, foramina 

 nervina, and thus, as a series of bundles, enter the overlying epi- 

 thelium in the region of the inner hair-cells. As they issue from 

 the connective tissue of the lip the fibres lose neurilemma and 

 medulla, and enter the epithelium as naked axis-cylinders. 



Concerning the farther course and ultimate endings of the 

 nerve there is much diversity and uncertainty of opinion ; but 

 the following account is probably the one deserving the greater 

 amount of confidence. 



The axis-cylinders, passing into the epithelium in the region of 

 the nuclear layer beneath the inner hair-cells, split up into fibrillae 

 and bundles of fibrillae. Some of these changing their course from 

 a radiate to a longitudinal, spiral one, contribute to form a strand 

 of fibrillae which runs in a spiral along the length of the cochlea, 

 in the nuclear layer at the base of the inner hair-cells, and may 

 be seen in vertical sections as a group of dots in this position 

 (Fig. 179 i.sp.n.) ;it is known as the inner spiral strand. Fibrillae 

 from this strand, or coming directly from the entering axis 

 cylinders, invest the bases of the inner hair-cells with nests of 

 fibrillae, very similar to those which invest the hair-cells of the 

 crista and macula. 



Other fibrillae passing between the limbs of the inner rods of 

 Corti, give rise to a second spiral strand lying within the tunnel 

 close to the inner rods (Fig. 179 t.sp.n.). This is known as the 

 spiral strand of the tunnel. 



Other fibrillae again, possibly connected with or joined by 

 fibrillae from the tunnel strand just mentioned, traverse the tunnel 

 in a radiate direction, pass between the limbs of the outer rods, 

 and form beneath the bases of the outer hair-cells proper, that is 

 the cells of Corti, at the level where the bodies of the cells of Corti 

 and of Deiters join each other, four outer spiral strands (Fig. 

 179 O.sp.n.), one for each row of hair-cells. From these spiral 

 strands or in connection with these spiral strands, fibrillae invest 

 the bases of the cells of Corti with nervous nests similar to those 

 belonging to the inner hair-cells. 



So far therefore as can be at present ascertained the fibres of 

 the auditory nerve end in fibrillae which form nests around both 

 the inner and outer hair-cells ; and if we accept the view laid down 

 in 827 we may say that the mode of ending of the cochlear 



