112 THE MEMBKANOUS LABYRINTH, BY PROF. RUDINGER. 



made in Fishes between the easily isolable axis-cylinder of the 

 ampullary nerves and that of the fibres entering the epithelium, 

 no histological difference is perceptible. With the use of 

 high powers, I believe I have observed the simple division of 

 the pale fibres in Frogs and Fishes even before the passage 

 through the basement membrane. Further subdivision, how- 

 ever, always takes rjlace after they have traversed it. 



The layer of nerve-epithelium on the roof of the ampullary 

 wall, that sometimes appears smooth, as in Man, Mammals, and 

 Birds, sometimes folded, as in Fishes, varies in thickness in 

 different animals from 0*016 of a millimeter (Bird) to 0*080 of 

 a millimeter (Cyprinoid Fishes). In Mammals and in Man its 

 thickness is intermediate to that of Birds and Fishes. The 

 deepest layer of the nerve-epithelium resting on the basement 

 membrane is soft, loose, and nucleated. It is thickest at the 

 centre, and is bounded towards the free border by a well-marked 

 line of demarcation, which resembles the membrana limitans 

 externa of the human eye, and upon these the stiff hairs are 

 seated. In the cyprinoids, Lang has described a peculiar cell 

 layer which I have occasionally seen with great distinctness. 

 These cells line the inner side of the epithelial layer ; and to 

 these the auditory hairs are attached. I regard the cavities in 

 the epithelium, described and depicted by Lang, as accidental 

 formations. The nerve-epithelium in the planum semilunare 

 of the Fish becomes gradually wider from below upwards ; then 

 again narrower, and runs out, as seen in transverse sections, into 

 a pointed extremity, to which the pavement cells of the upper 

 portion of the ampulla are applied. Furthermore, at the point 

 of transition of the crista acustica into the planum semilunare 

 there is a less elevated epithelial layer. (See fig. 310.) The 

 crista cruciata of the ampulla of the Bird, which projects to a 

 considerable extent into the interior of the cavity, is covered 

 throughout its whole extent by a rather thin layer of nerve- 

 epithelium. 



In the sacculi the nerve-epithelium is usually somewhat 

 lower than in the ampullae. Its transition into the adjoining 

 columnar epithelium is here also more gradual ; whilst in the 

 sacculus rotundus, even at those parts which receive no nerves, 

 the epithelium never presents so flattened a form as in the 



