No. I.] THE VERTEBRATE EAR. 93 



secreting the tectorial membrane. It never leaves these cells, 

 but lies upon them throughout life, except the anterior ends." 



It is of a soft almost mucous consistency, withstands tearing 

 with considerable force, and swells much in hydrochloric acid. 

 The fibrillas are separable, and there is probably an inter-fibrillar 

 ground substance. In that portion of the lower face in contact 

 with the teeth, one finds meshes of a network impressed on the 

 surface. Corti's division of the membrane into four zones can, 

 although they are usually present, be referred (H.) to external 

 and secondary influences, and hence may be disregarded. The 

 part lying on the teeth is relatively very thin. Not only is the 

 thickness of the membrane subject to great variation, — depend- 

 ing on the height of the teeth or of the papilla or the sulcus 

 epithelium, but also in the different parts of the same cochlear 

 canal. At the hamulus and radix the membrane ends in a some- 

 what pointed and dentate manner corresponding to the end of 

 the teeth and the papilla. 



In breadth it increases as the hamulus is approached. The 

 proximal edge lies in the line of origin of the memb. Reissneri. 

 In the pig, however, it passes up onto this membrane a few cells 

 breadth. The outer border was always found in adult human 

 ears not to overlap or pass beyond the outer row of Corti's cells. 

 It is at any rate certain that the membrane of Corti is fixed 

 from the teeth over the lower wall of the sulcus, and outward 

 from this lies free upon the rods of the lamina reticularis. 



Loewenberg (1864, 185) : The membrana Cortii shows three 

 zones, — an inner, a middle, and an outer. The inner has no 

 transverse striations and no network imprinted on its under sur- 

 face. The middle zone has both. The striations really run 

 obliquely to cross-section. They lie in several layers, and are 

 arched over Corti's organ. Besides these I found a peculiar 

 " accessory layer," which extended from the second third out- 

 ward. This structure looked like a much perforated lamella, 

 forming now and then a tissue of broad stripes. These stripes 

 are nearly parallel to one another, and run in one direction, which 

 nearly coincides with the border of the membrane. In sections, 

 however, one sees that the perforations are in reality only thin 

 places in the membrane, and the stripes are thickenings. In- 

 ternally, this layer becomes very thin and its commencement 

 very difficult to trace. Externally, it grows thicker and forms 



