396 NORMAL HISTOLOGY. 



peripheral spiral canal within the base of the bony spiral lamina. 

 Within the peripheral canal the nerve-fibres are augmented by 

 numerous nerve -cells, continuing along the spiral canal as the 

 ganglion spirale. From this numerous twigs are given off, which 

 pass along the canals within the spiral lamina towards its margin, 

 the twigs meanwhile subdividing to form an extensive plexus con- 

 tained within corresponding channels in the bone. At the edge of 

 the spiral lamina bundles of fine fibres are given off, which escape at 

 the foramina nervina and enter the epithelium close to the inner 

 rod of Corti. During or before their passage through the foramina 

 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 inner 

 side of the base of the inner pillar, where they divide into two 

 sets of fibrillse, one going to the inner hair-cells, the other passing 

 between the inner pillars to reach the tunnel. After crossing this 

 space the fibrillae escape between the outer rods into the epithe- 

 lium lying on the outer side of the arch. The further course of the 

 fibrillse seems to be such that some fibrillse extend between the 

 outer pillar of Corti and the first row of hair-cells, while succeeding 

 groups of fibrillae course between the rows of Deiters's cells to reach 

 the remaining hair-cells. The exact relation between the nerve- 

 fibrils and the auditory cells, as to whether the fibrillae actually join 

 the cells or only come in close contact, is yet a matter of uncertainty, 

 although renewed investigations render it still improbable that direct 

 anatomical continuity exists. 



The ductus and saccus endolymphaticus possess walls which 

 closely correspond with those of the saccule and the utricle, com- 

 posed of a thin connective-tissue tunica propria supporting the 

 lining of ectodermic epithelium ; the latter consists of a single 

 layer of flat polyhedral cells. The duct lies within the bony 

 aqueduct, closely united with the periosteal lining, unsurrounded by 

 an extension of the perilymphatic space ; in a few localities a meagre 

 layer of loose connective tissue forms a less intimate bond between 

 the periosteum and the fibrous coat of the duct. 



The cochlear perilymphatic spaces, the scalae vestibuli et 

 tympani, include within their walls the same tissues that bound 

 similar cavities within other parts of the internal ear. The perios- 

 teum of the bony cochlea constitutes the fibrous tunic, which is 

 usually covered on the surface in contact with the enclosed perilymph 

 by a single layer of endothelial plates ; in some localities, however, 

 as on the tympanic surface of the basilar membrane, the lining cells 

 retain their primitive mesodermic character, never becoming fully 

 differentiated into endothelium. 



