214 



PHYSIOLOGY 



CHAP. 



(Fig. 82), bounded laterally by the bony walls of the cochlea 

 lined with periosteum, superiorly by Keissner's membrane, 

 inferiorly by a small portion of the lamina spiralis and the 

 basilar membrane. The lamina spiralis terminates in a sickle- 

 shaped edge (limbus}, which has the form of a C in section, with 

 the under lip projecting and more sharply pointed than the upper. 

 The bay is known as the spiral groove, 



The basilar membrane completes the floor of the cochlear 

 canal, being attached on one side to the lower margin of the 



FIG. 82. Section across the basal turn of the human cochlea. Magnified. (G. Retzius.) D.C., 

 ductus cochleae; s.v., scala vestibuli ; s.t., scala tympani ; R., membrana Reissneri ; M.t., 

 membrana tectoria ; b.m., membrana basilaris ; str.v., stria vascularis ; l.sji., ligamentum 

 spirale; L, limbus; s.sp., sulcus spiralis; t.C., tunnel of Corti ; h.i., inner hair-cells; Ji.e., 

 outer hair-cells ; -., nerve-fibres ; sp.l., spiral lamina. 



limbus, on the other to the spiral ligament, which appears in 

 section to be a triangular projection of fibrous connective tissue 

 attached to the periosteum of the outer wall of the cochlea. It 

 is an important anatomical fact that the basilar membrane 

 increases in width from the base to the apex of the cochlea, 

 while the breadth of the bony spiral lamina diminishes propor- 

 tionately. According to Hensen, the basilar membrane at the 

 base of the cochlea occupies a narrow cleft about 0-041 mm. 

 across, while at the apex it measures 0-495 mm., that is, about 

 twelve times wider than the base. There are two zones in the 

 basilar membrane : the zona arcuata, to the edges of which the 



