INNERVATION. 



[CHAP. xvin. 



Fig. 142. 



ably smaller, so that the peri- 

 lymph intervenes in some quan- 

 tity, except where the nerves pass- 

 ing to it confine it in close con- 

 tact with the osseous wall. Its 

 vestibular portion consists of two 

 sacs, viz. : a principal one of trans- 

 versely oval figure and compressed 

 laterally, called the utriculus or 

 common sinus, occupying the upper 

 and back part of the cavity, in 

 contact with the fovea semi-ellip- 

 tica, and beneath this a smaller 

 and more globular one, the sac- 

 culus, lying in the fovea hemi- 

 spherica, near the orifice of the 



Membranous labyrinth of the left side, with its Vestibular SCala of the COClllea, 



nerves and otoliths: su. Superior semicircular , , , , . . T 



canal, with the ampulla and its nerve at one end, and probably Communicating With 



and the other end joined by />, the posterior canal, , . , 



to form the tubulus communis, i. Inferior, or the UtriCUlUS. 



horizontal canal, with the ampulla and its nerve at m i , . . 7 



one end, and the other entering the utriculus sepa- 1 he memOTaHOUS SemiClTCU iCLT 



rately. c. Powdery otolith seen through the trans- 7 -, . , -i 



lucent wall of the common sinus, or utriculus, with Canals have the Same naniCS, Shape, 



the nerves distributed to it. s. Powdery otolith of j , , 



the sacculus seen with its nerve, in a similar way. and arrangement as the OSSCOUS 



n. Cochlear division of the auditory nerve cut off i i i i xt, "U 4. 



where it enters the cochlea, d. Portio dura of the CanalS Which CnClOSC them, DUt are 



seventh pair leaving the auditory nerve, or portio T .-i -, / ,-, -j n 



mollis, to enter the aqueduct of Fallopius. Mag- Only a third OI the diameter Ol 



the latter. As the osseous canals 



open into the vestibule, so the membranous ones open at both ends 

 into the utriculus there being, however, a constricted neck between 

 this sac and the ampullated extremity of each canal. The auditory 

 nerve sends branches to the utriculus, to the sacculus, and to the am- 

 pulla of each membranous canal. These nerves enter the vestibule by 

 the minute apertures before described, and tie down, as it were, both 

 the utriculus and sacculus to the osseous wall at those points, the 

 membrane being much thicker and more rigid where the nerves join 

 it. The branches to the ampullae of the superior vertical and the 

 horizontal semicircular canals enter the vestibule with the utricular 

 nerve, and then cross to their destinations, while that to the ampulla 

 of the posterior vertical canal traverses the posterior wall of the 

 cavity and opens directly into the ampulla. 



The wall of the membranous labyrinth is translucent, flexible, and 

 tough. When withdrawn from its bed and examined, it appears to 

 present three coats, an outer, middle, and internal. The outer is 

 loose, easily detached, somewhat flocculent, and contains more or 



