532 THE SOLIDS. 



are deposited. It has a regular arrangement, and is not free 

 to change its place in the endolymph. Otolithes consist 

 always of carbonate of lime. 



Of the Vestibular Nerves. " In consequence of the thick- 

 ness of the wall of the membranous labyrinth where the 

 nerves enter, and the presence there of the calcareous and 

 fibrous matter, it is not easy to ascertain with certainty the 

 precise manner in which the nerves terminate. In the utri- 

 cule and saccule, they appear to spread out from one another 

 as they enter, and then to pass, some to mingle with the 

 calcareous powder, others to radiate for a small extent on the 

 inner surface of the wall of the cavity, where they come into 

 connection with a layer of dark and closely set nucleated 

 cells, and presently loose their white substance. We have 

 seen a fibrous film on the inner surface of these parts which 

 we are disposed to consider as formed, like the inner surface 

 of the retina, by the union of the axis-cylinders of the nerve 

 tubes, but confirmatory observations are required. Those 

 that traverse the calcareous clusters have appeared to us, in 

 the most lucid views we have succeeded in obtaining, to 

 terminate by free, pointed extremities, without losing their 

 white substance. In the frog this has been evident enough. 

 " The nervous twigs belonging to the semicircular canals 

 do not seem to advance beyond the ampullae, in which they 

 have a remarkable distribution, entering them, as Steifen- 

 sand has well shown, by a transverse or forked groove, on 

 their concave side, and which reaches about a third round. 

 Within this, the nerve projects so as to form a sort of trans- 

 verse bulge within the ampulla. Their precise termination 

 can be best seen in the osseous fishes, and has been de- 

 scribed by Wagner to be loop-like. We believe we have 

 seen this mode of termination, though certainly never so 

 plainly as the figure given by this excellent author would 

 indicate ; and we may add that we have found free extrem- 

 ities to the nerve tubes, as well as loopings, in the ampullae 

 of the cod. The difficulty in these cases of ascertaining the 

 exact truth arises from the curves formed by the nerve tubes 



