No. I.] THE VERTEBRATE EAR. , 41 



The cochlear organ thus appears to be made up of a large num- 

 ber of similar hair cells in the form of an even plate. 



Although both Retzius and Hasse conclude that in the papilla 

 basilaris of the bird we do not have a genuine organ of Corti, 

 they consider the membrana tectoria of this organ as the homo- 

 logue of the membrana Cortii of the mammalian ear. 



Retzius describes this membrane as a somewhat soft, homo- 

 geneous, gelatinous skin, whose substance is perforated with 

 many holes. In cross-section triangular, it varies in different 

 parts of the organ, both in size and shape. He figures (PI. 

 XVIII, Fig. 13) two very distinct parts, which he describes as 

 having somewhat different structures. That part {^7its}j which 

 lies against the clear cylinder cells of the inner border of the 

 organ has its long axis placed perpendicularly with the basilar 

 membrane, while the larger part (;;z^.), or the membrana tectoria 

 propria, always lies with its long axis (in cross-section) placed 

 parallel with the surface of the basilar papilla, as is readily seen 

 from his figures. The tectorial membrane lies somewhat above 

 the surface of the sensory cells, so that a narrow cleft is left 

 between them, into which (across which) the hairs project. 

 The membrane does not extend to the inner border of the 

 papilla, and consequently three or four rows of the inner hair 

 cells are left uncovered. The other hairs come in contact with 

 the surface of the membrane, and in many cases seem to pro- 

 ject into the holes of the membrane. These inner hairs Retzius 

 found covered by the peculiar long hyaline cells. The membrane 

 reaches quite to the outer border of the sense organ. As the 

 nature of the tectorial membranes will be discussed in another 

 chapter, it will suffice to say here that Retzius did not observe the 

 tectorial membrane in its living condition and normal relations. 



The tectorial membrane of the lagenar organ is apparently 

 composed of the irregular network of fibres inclosing numerous 

 otolith crystals, especially in its upper part. The otoliths lie 

 either on the surface of the network or partly imbedded in it. 

 Such is the appearance of the membrane as a whole in ordinary 

 preparations of the ear. 



Alligator (PL X, Figs. 3 and 4). 



The sense organ of the lagenar portion of the cochlea rises 

 gradually from the lining epithel of the lagenar chamber. It 



