84 INNEllVATION. [CHAP. XVIII. 



Of the Vestibular Nerves. In consequence of the thickness 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 ter- 

 minate. In the utricle 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 connexion 

 with a layer of dark and closely-set nucleated cells, and presently 

 lose 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-cylin- 

 ders 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 sub- 

 stance. In the frog this has 

 been evident enough. 



The nervous twigs belong- 

 ing to the semicircular canals 

 do not seem to advance be- 

 yond the ampullae, in which 

 they have a remarkable dis- 

 tribution, entering thern, as 

 Steifensaiid has well shown, by 

 a transverse or forked groove 



View of the nerves going to the membranous laby- , r i i 



rinth: . Branch to the ampulla of one of the semi- Oil their COUCaVC Side, and 



circular canals. It is seen perforating the wall and 1-1 i r, j. J.-L 3 



expanding transversely within. 6. Semicircular canal Which readies aDOUt a third 



round. Within this, the nerve 



projects so as to form a sort of transverse bulge within the am- 

 pulla. Their precise termination can be best seen in the osseous 

 fishes, and has been described by Wagner to be looplike, as will be 

 apparent from the adjoined figure. 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 extremities 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 in proceeding to their destination, and which are 

 liable to be mistaken for terminal loopings. 



