CHAP. XVIII.] THE COCHLEAR NERVES. 81 



The scabe of the cochlea are lined with a nucleated membrane, 

 or epithelium, which is very delicate and easily detached, usually 

 more easily seen in the vestibular than in the tympanic scala, and 

 in many animals containing scattered pigment. 



Of the Cochlear Nerves. These enter from the internal auditory 

 meatus, through the spirally-arranged orifices at the base of the mo- 

 diolus, and turn over in succession into the Fig , 41 



canals hollowed in the osseous zone of the spiral 

 lamina, close to its tympanic surface. In this 

 distribution, the nervous bundles subdivide and 

 reunite again and again, forming a plexus with 

 elongated meshes, the general radiating arrange- 

 ment of which can be readily seen through the 

 substance of the bone when it has been steeped 

 in diluted hydrochloric acid (fig. 141). Towards 

 the border of the osseous zone the bundles of 

 the plexus are smaller, and more closely set, 

 so as at length almost to form a thin uniform 

 layer of nervous tubules. Beyond the border, 

 and partially on or in the inner transparent belt 

 of the membranous zone, these tubules arrange 

 themselves more or less evidently into small 

 sets, which advance a short distance and then gan giTon aci giobuics re in re thi8 

 terminate much on the same level. These ter- ffi3 SS! T^ $ 



-iipj-ii i 3 , cochlear nerve in the modio- 



mmal sets or tubules are cone-shaped, 'coming to lus, u^ fibres diverging and 



a kind of point ere they cease. The white sub- 



stance of Schwann exists in them throughout, 



but is thrown into varicosities and broken with 



extreme facility, and they are interspersed with 



nuclei, so that it is very difficult to discover the 8tieep ' Magnil 



precise disposition of the individual tubules (fig. 139, a) . They seem 



to cease one after another, thus causing the set to taper ; and at 



least it appears certain that evidence of loopings, such as have been 



described by some, is wanting. In the cochlea of the bird, however, 



we have seen at one end a plexiform arrangement of nucleated fibres 



ending in loops ; but this is a peculiar structure. 



The capillaries of the osseous zone are most abundant on the 

 tympanic scala, in connexion with the nerves now mentioned, and 

 form loops near the margin, with here and there an inosculation 

 with the large marginal capillary already mentioned. 



Of the Membranous Labyrinth (fig. 142). This has the same 

 general shape us the bony cavities in which it lies, but is consider- 



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