373 



NORMAL HISTOLOGY. 



onal areas of the end-plates of Deiters' cells (Fig. 425). The outer hair-cells are cylin- 

 drical in their general form, terminating about the middle 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 support- 

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

 the membrana reticularis. The deeper end of each outer hair-cell contains a dense 

 yellowish enclosure, known as the body of Retzius, 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 

 specialized sustentacular epithelial cells which extend the entire thickness of the epi- 

 thelial stratum to terminate in the peculiar end-plates or phalanges. It follows, that 

 while the free surface of Corti' s organ is composed of both auditory and sustentacular 



Cells of Hensen 



- Deiters' cells 



Outer hair-cells 



Plate-like processes of 

 inner pillar-cells 



Outer pillar cells 

 Inner hair-cells 



FIG. 425. Corti's organ viewed from above, showing mosaic formed by pillars and Deiters' cells; outer 

 ends of auditory cells occupy meshes of cuticular network. (Relztus.) 



cells, the elements resting upon the basilar membrane are of one kind alone the cells 

 of Deiters. The bodies of the latter consist of two parts, the elongated cylindrical 

 thief portion of the cell, containing the spherical nucleus and resting upon the basilar 

 membrane, and the greatly attenuated pyramidal phalangeal process. A system of 

 communicating intercellular clefts, the spaces of Nuel, lie between the auditory and 

 supporting cells ; like the tunnel of Corti, these spaces are occupied by a semifluid in- 

 tercellular substance. The cells of Deiters are arranged, as a rule, in three rows, al- 

 though in places within the upper turns four or even five alternating rows are some- 

 times found. Each cell contains a fine filament, the fibre of Retzius, which begins 

 near the middle of the base with a conical expansion and extends through the cell- 

 body to the apex of the phalangeal process. 



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 conspicuous position over the organ of Corti. 

 The membrane seems to be composed of fine resistent fibres, held together by an in- 

 terfibrillar 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 modelled 

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

 the sttipe of Hensen. Like the basilar membrane, the membrana tectoria increases in 

 width from the base towards the apex of the cochlea. 



