THE INTERNAL EAR. 



1521 



FIG. 1274. 



(Fig. 1274). The outer hair-cells are cylindrical in their general form, terminating about the mid- 

 dle of the epithelial layer in slightly expanded rounded ends, near which the spherical nuclei are 

 situated. The outer sharply defined ends of the cells are distinguished by a cuticular border sup- 

 porting about twenty-five rigid auditory rods or hairs which project beyond the level of the mem- 

 brana reticularis. The deeper end of each outer hair-cell contains a dense yellowish enclosure, 

 known as the body oj 'Retzizis, which is triangular when seen in profile. The bodies are absent 

 in the inner hair-cells. 



The cells of Deiters have much in common with the rods of Corti, like these being special- 

 ized sustentacular epithelial cells which extend the entire thickness of the epithelial stratum to 

 terminate in the peculiar end-plates or phalanges. It follows, that whilst the free surface of Corti's 

 organ is composed of both auditory and sustentacular cells, the elements resting upon the basi- 

 lar membrane are of one kind alone the cells of Deiters. The bodies of the latter consist of 

 two parts, the elongated cylindri- 

 cal chief portion of the cell, con- 

 taining the spherical nucleus and 

 resting upon the basilar mem- 

 brane, and the greatly attenuated 

 pyramidal phalangeal process. 

 A system of communicating in- 

 tercellular clefts, the spaces of 

 Nuel, lie between the auditory 

 and supporting cells ; like the 

 tunnel of Corti, these spaces are 

 occupied by a semifluid intercel- 

 lular substance. The cells of 

 Deiters are arranged, as a rule, 

 in three rows, although in places 

 within the upper turns four or 

 even five alternating rows are 

 sometimes found. Each, cell 

 contains a fine filament, ihejibre 

 ofRetzius, which begins near the 



Cells of Hensen 



' Deiters' cells 



Outer hair-cells 



Plate-like processes of 

 inner pillar-cells 



Outer pillar cells 

 Inner hair-cells 



Corti's organ viewed from above, showing mosaic formed by pillars 

 and Deiters' cells ; outer ends of auditory cells occupy meshes of cuticular 

 net-work. (Retzius). 



middle of the base with a conical 



expansion, and extends through 



the cell-body to the apex of 



the phalangeal process, where, 



according to Spec, it splits into seven or more fine end-fibrils, that extend into the cuticular 



superficial layer under and about the phalanges. 



The membrana tectoria or Corti's membrane stretches laterally from the upper lip of the 

 limbus, above the sulcus spiralis and Corti's organ, as far as the last row of outer hair-cells. 

 The membrane is a cuticular production, formed originally by the cells covering the region of 

 the auditory teeth and the spiral sulcus. Medially it rests upon the epithelial cells, but farther 

 outward it becomes separated from the free edge of the auditory teeth and assumes its conspic- 

 uous position over the organ of Corti. The membrane seems to be composed of fine resistant 

 fibres, held together by an interfibrillar substance. During life the membrane is probably soft 

 and gelatinous, and much less rigid than its appearance indicates after the effect of reagents. 

 The lower surface of the free portion of the membrane, opposite the inner hair-cells, is mod- 

 elled by a shallow furrow, which indicates the position of a spirally arranged band known as the 

 stripe of Hensen. Like the basilar membrane, the membrana tectoria increases in width from 

 the base towards the apex of the cochlea. 



The outer sustentacular cells or cells of Hensen form an outer 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. They do not contain the fibres of Retzius. 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 simple row of cuboidal cells possessing clear, faintly granular protoplasm and spherical nuclei. 



The Nerves of the Cochlea. The branches of the cochlear division of the 

 auditory nerve enter the base of the cochlea through the tractus spiralis foraminosus 

 (page 1514), those destined for the apical turn traversing the central canal of the 

 modiolus. From the modiolus a series of stout lateral branches diverge at quite 

 regular intervals through canals which communicate with the peripheral spiral canal 

 within the base of the bony spiral lamina. Within the peripheral canal the nerve- 

 fibres join numerous aggregations of bipolar nerve-cells, which continue along the 



96 



