238 



ANATOMY OF VERTEBRATES. 



Nerves of ampulla; and ' sinus communis;' magn. 

 Human, xcix". 



181 



B 



respective waves of sound must strike upon the rich supply ot 

 nerves at the ampullary ends, may have relation to the power 



of appreciating the locality of 

 the source of sound, or the di- 

 rection in which it arrives. The 

 branch, fig. 180, y, to the ' com- 

 mon sinus ' spreads thereon in a 

 radiated expanse : the branches, 

 o, p, to the ampullae of the 

 upper, , and horizontal, b, 



canals, form a bifurcate enlarge- 

 ment, p, upon their outer surface. 

 When the ampulla is laid open, 

 as in fig. 181, the nervous fork 

 is seen to protrude and push 

 in a slightly curved eminence 

 of the membrane, ib. A, upon 

 which and the adjacent part of the ampulla the delicate ner- 

 vous fibres resolve them- 

 selves into a kind of retinal 

 pulp, ib. C. 



The septal plate of the 

 cochlea has lent itself to a 

 more favourable or distinct 

 view of the termination of 

 the acoustic fibrils. Fig. 182 



Terminations of nerves in ampullae, magn. Human. 



XCIX "- shows the cochlear nerve, 



isolated. If a small bit of the spiral plate, fig. 183, A, be magni- 

 fied, as at B, the filaments, b, are seen, as they diverge upon 



the osseous part, to sub- 

 side or flatten on ap- 

 proaching the middle 

 tract, and there to anas- 

 tomose in loops, c ; the 

 neurilemma, d, being 

 continued on to blend 

 with the membranous 

 part of the spiral plate. 

 The human tympanic 

 cavity, fig. 184, is formed 

 by the petrosal,the mas- 

 toid, and the tympanic 

 bone: in the dry skull ; t 



182 



The cochlear nerve, magn. xcvi" 



