392 



ELEMENTARY PHYSIOLOGY 



LESS. 



(i) The Membranous Labyrinth. — The membranous 

 bag, as we have said, is not simple but complicated ; 

 it consists of several parts. In the first place there 

 is a somewhat oval sac, called the utricle (Fig. 

 123, Ut.) into which open three hoop-like semicircular 

 canals. Of these two are placed vertically, one directed 

 anteriorly, the other posteriorly, and are hence called the 



A.// 



Fm. 124. 



Diagram to ilhistrate the endings of the auditory nerve In the mem- 

 branous labyrinth and cochlea. N.B. The drawinii i.f diagramiuatic. 



A.N, auditory nerve dividing into several branches, and ending: — at 

 A.a.C, in the ampulla of the anterior vertical semicircular canal : P.S.C, 

 do. posterior vertical: S.S.C, do. external horizontal: I/, in the utricle: 

 S, in the saccule. Cock, the ending all along the canalis cochlearis ; 

 A.V, canal uniting the interior of utricle with that of saccule. C, 

 canal joining the saccule to the canalis cochlearis. 



anterior {P. A) and posterior (P. F) vertical semi- 

 circular canals. Tlie third is placed horizontally and 

 directed outwards, hence it is called the exterior 

 horizontal semicircular canal (Fig, 123, H). It 

 will be observed that the three canals thus lie in the three 

 directions of space. Each of these three hoops is 



