124 



THE EAR. 



membrane. In its situation relative to the auditory epithelium it corresponds to 

 the otolithic accumulations of the maculae. 



Nerves of the cochlea. The branch of the auditory nerve which goes to the 

 cochlea is given off in common with those to the saccule and the posterior ampulla, 



Fig. 142. GENERAL VIEW OF THE MODE OF DIS- 

 TRIBUTION OF THE COCHLEAR NERVE, ALL THE 

 OTHER PARTS HAVING BEEN REMOVED. (Arnold.) 



It is shorter, flatter, and broader than any 

 of the other branches. It perforates the 

 bone by groups of minute foramina at the 

 bottom of the internal meatus, below the 

 opening of the Fallopian aqueduct. These 

 groups are arranged in a shallow spiral 

 furrow (tractus spiralis foraminulentus) in 

 the centre of the base of the cochlea ; and 

 they lead into small bony canals, which 

 first follow the direction of the axis of the 



cochlea, through the modiolus, and then radiate outwards, between the plates of the 

 the bony spiral lamina (fig. 129). In the centre of the spiral tract is a larger foramen 

 which leads to the central canal of the modiolus. Through this foramen and canal the 



Fig. 143. DISTRIBUTION OF THE COCH 



LEAR NERVES IN THE SPIRAL LAMINA. 



(After Henle.) 



This figure shows part of the modiolus 

 and spiral lamina, viewed from the base, 

 showing the plexiform arrangement of the 

 cochlear nerves ; 1, filaments of the nerve 

 issuing from the tractus spiralis foraminu- 

 leiitus ; 2, branches of the nerve entering 

 the central canal of the modiolus ; 3, wide 

 plexus in the bony lamina spiralis j 4, 

 close plexus at its border. 



Fig. 144. PART OF THE NERVES EX- 

 TRACTED AND MORK HIGHLY MAGNI- 

 FIED. 



2, twigs of the nerve from the 

 modiolus close to the lamina spiralis 

 ossea ; ys, spiral ganglion ; /?, nerve- 

 fibres running spirally along the outer 

 part of the ganglionic swelling 3, wide 

 plexus ; 4, close plexus of nerve-fibres as 

 in fig. 143. 



filaments for the last half- turn of 

 the spiral lamina are conducted ; 

 whilst the first two turns are 

 supplied by the filaments which 



occupy the smaller foramina and bent canals. 3Tear the root of the spiral lamina 

 the nerve-fibres pass outwards through a spirally wound ganglionic cord (ganglion 

 spirals), situated in the special bony canal (spiral canal of the modiolus) already 

 mentioned. The cells of this ganglion are bipolar and each nerve-fibre appears 

 to have one of the cells interpolated in its course. From the outer side of the 

 ganglion, the fibres, having resumed their medullary sheath, pass onwards with a 

 plexiform arrangement, at first in distinct but anastomosing cords (fig. 144, 3), 



