ORGANS OP THE SENSES. 529 



the tympanic scala, and in many animals containing scat- 

 tered pigment. 



Of the Cochlear Nerves. " These enter from the internal 

 auditory meatus through the spirally arranged orifices at the 

 base of the modiolus, and turn over in succession into the 

 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 may be readily seen through the substance of 

 the bone when it has been steeped in diluted hydrochloric 

 acid. (Plate LXIX.jfy. 6.) 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 terminate much 

 on the same level. These terminal sets of tubules are cone- 

 shaped, coming to a kind of point ere they cease. The white 

 substance 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 precise disposition of the individual tubules. 

 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 connection with the nerves now men- 

 tioned, and form loops near the margin, with here and there 

 an inosculation with the large marginal capillary already 

 mentioned. 



Of the Membranous Labyrinth. " This has the same 

 general shape as the bony cavities in which it lies, but is 

 considerably smaller, so that the perilymph intervenes in 



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