THE SENSE OF HEAEING 



217 



the point of origin of the inner rods, and wind spirally round the 

 bases of Corti's and Deiters' cells (Fig. 85). 



To complete the description of the organ of Corti we must 

 notice in conclusion the tectorial membrane, to which secondary 

 importance has erroneously been ascribed. The membrana tectoria 

 rises on the crest of the ' limbus in the form of a thin membrane, 

 which subsequently swells in a pad-like projection over the spiral 

 groove, the rods of Corti, and the inner and outer hair -cells 

 (Fig. 86). From the surface it appears distinctly fibrous, with 

 obliquely slanting fibrils and a scalloped 

 edge identical in structure with the sub- 

 jacent membrana reticularis. Many authors 

 (Gottstein, Hensen, Eetzius, Siebemnann) 

 hold that the outer zone of the tectorial 

 membrane terminates in a free edge, which 

 floats in the perilymph a short distance 

 from the ends of the hairlets of the hair- 

 cells. Eetzius, however, found in embryos 

 of rabbits and cats that the outer edge of 

 the tectorial membrane is anatomically con- 

 nected with the most peripheral cells of 

 Deiters, although this union disappears in 

 adult animals. This statement was con- 

 firmed by Schwalbe. Others, again, found 

 an indefinite anatomical connection in 

 adults between the membrana tectoria and 

 the underlying organ of Corti (Boettcher, 

 Earth, Czinner, Haminerschlag). More 

 recently (1907) Kishi has shown in some 

 histological preparations that the tectorial 

 membrane is united in adults, too, with the 

 outer surface of the reticular lamina, which 

 often escapes notice because this membrane 

 is normally excessively tense, and retracts, 

 and becomes torn, in the fixing fluid. 

 According to Kishi the normal form of the 

 organ of Corti is that represented in Fig. 87, in which the hairlets 

 of the internal and external hair-cells stand vertically to the mem- 

 brana tectoria, with which they are in immediate contact. The outer 

 edge of this membrane is connected with the end of the membrana 

 reticularis ; when this is stretched, the tectorial membrane is of 

 uniform thickness over its whole extent ; finally, the rods of Corti 

 form an almost equilateral triangle with the basilar membrane from 

 which they spring. The increased thickness of the organ of Corti 

 in its outer part in most preparations depends on the elastic re- 

 traction it undergoes after rupture of its external border, which 

 also causes deformation of the arches of Corti formed by the rods. 



FIG. 86. Surface of small portion 

 of membrana tectoria of human 

 cochlea. (G. Retains.) l.z., 

 limbus - zone of membrane ; 

 traces of cells covering the 

 limbus; o.z., o.z., outer zone 

 showing fibrous structure ; 

 H., Hensen's band; /., free 

 reticular edge. 



