No. I.] THE VERTEBRATE EAR. 8 1 



Alligator we find that the nerve distribution is, as far as the 

 external branch is concerned, fundamentally the same as in 

 mammals. For instance, in the Alligator the nerve enters 

 through the cartilaginous supporting bar at the inside of the 

 Sauropsid acoustic papilla, and piercing the cartilage passes out 

 underneath the inner hair cell row, to which it gives off fibres, 

 under the main plate of the cochlear organ, and here disappears 

 at the bases of the cells. As the fibres approach the bases 

 of the hair cells, which here rest on the cushion formed by 

 the supporting cells of the organ, they lose their medullated 

 sheaths, and passing upwards, pierce the upper layers of the 

 supporting cushion, reaching finally the bases of the hair cells, 

 probably penetrating into their substance, and entering into 

 direct communication with their nuclei as in the mammalian 

 cochlea. The fibres which pass beyond the row of inner 

 hair cells cross obliquely the space outside these cells and dis- 

 appear among the outer hair cells. The hairs which are given 

 off at the top of the cells appear to be thicker and shorter 

 than the hairs of the corresponding cells in the mammalian 

 ear, and consequently the membrana tectoria which they form 

 is a wider band relatively, but neither absolutely nor relatively 

 as thick. It is also thickest in its middle part, thinning off 

 both ways. 



The inner row of outer hair cells of the mammalian cochlea 

 shows much more than the inner hair cells, the same form of 

 body and relation to supporting cells and basilar membrane 

 that the remaining hair cells of the organ of Corti display ; 

 indeed, they may be said to have progressed beyond them 

 but little except in the more perfect isolation of the cells and 

 the consequent greater separation of the hairs of the row. 

 The isolation cells are not so distinct and do not play as impor- 

 tant a part in the separation and support of the cells beyond 

 the second row as they do between the first two rows of inner 

 hair cells ; they are, however, much advanced beyond the con- 

 dition of development, in which they exist between the cells of 

 the outer, unmodified portion of the papilla basilaris. Here 

 they present the simple unmodified condition which character- 

 izes them in the maculae, cristae, and papillae of the other parts 

 of the ear. 



The pillars of Corti present in their development among the 



