THE INTERNAL EAR. 379 



The outer sustentacular cells or cells of Hensen form a zone immediately external 

 to the last Deiters' cells. These elements resemble the inner sustentacular cells, but 

 differ somewhat in form and arrangement. In consequence of their oblique position, 

 the bodies are not only greatly elongated, but also imbricated. The cells of Claudius 

 are the direct continuations of Hensen's cells, and laterally pass uninterruptedly into 

 the low columnar elements covering the remaining part of the basilar membrane. 

 They consist of a single row of cuboidal cells possessing clear, faintly granular proto- 

 plasm and spherical nuclei. 



The Nerves of the Membranous Labyrinth. The branches of 

 the cochlear division of the auditory nerve enter the base of the cochlea 

 through numerous small foramina, those destined for the apical turn travers- 

 ing the central canal of the modiolus. From the modiolus a series of stout 

 laceral branches diverge at quite regular intervals through canals which com- 

 municate with the peripheral spiral canal within the base of the bony spiral 

 lamina. Within the peripheral canal the nerve-fibres join numerous aggre- 

 gations of bipolar nerve-cells, which continue along the spiral canal and col- 

 lectively constitute the ganglion spirale. From these cells numerous den- 

 drites are given off, which pass along the canals within the spiral lamina 

 towards its margin, the twigs meanwhile subdividing to form an extensive 

 tract contained within corresponding channels in the bone. At the edge 

 of the spiral lamina, bundles of fine fibres are given off, which enter the epi- 

 thelial layer close to the inner rod of Corti. During or before their escape 

 from the lamina, the nerve-fibres lose their medullary substance and proceed 

 to their destination as fine naked axis-cylinders. The radiating bundles pass 

 within the epithelium to the mesial -side of the base of the inner pillar; here 

 they divide into two sets of fibrillae, one, the mesial spiral fasciculus, going 

 to the inner hair-cells and the other, the lateral spiral fasciculus, passing be- 

 tween the inner pillars to reach the tunnel of Corti. Within this space 

 fibrillae are given off which, after crossing the tunnel, escape between the 

 outer rods into the epithelium lying on the lateral side of the arch. The 

 further course of the fibrillae seems to be such that some extend between the 

 outer pillar of Corti and the first rows of hair-cells, whilst succeeding groups 

 of fibrillae course between the rows of Deiters' cells to reach the remaining 

 hair-cells. The relation between the nerve-fibrils and the auditory cells is 

 in all cases probably close contact and not actual junction. 



The nerves supplying the saccule, utricle, and the semicircular canals 

 are all fibres from the vestibular division of the auditory nerve. They 

 traverse the bony labyrinth through canals that open internally at certain 

 areas, the macula cribrosa, by numerous openings in close relation to the 

 specialized areas in the wall of the membranous labyrinth. The relations of 

 the nerve fibres to the receptive cells of these maculae and cristae have been 

 described (page 373). 



Blood-Vessels of the Membranous Labyrinth. The auditory 

 artery, a branch of the basilar, after entering the internal auditory meatus 

 divides into three branches, (i) The vestibular artery accompanies the 

 utriculo-ampullary nerve and supplies the upper part of the vestibule, includ- 

 ing the posterior part of the utricle with its macula, the saccule and the cristae 

 of the upper and outer ampullae of the corresponding semicircular canals. 

 (2) The cochlear artery pursues a spiral course. It gives off three branches, 

 two of which are distributed to the lower turn of the cochlea, while the 

 third supplies the middle and apical turns. (3) The ,vestibjilo-cochlear 

 artery arises either from the cochlear artery or independently and divides, 

 within the spiral lamina, into a cochlear and a vestibular branch. The 



