THE ORGAN OF HEARING. 441 



and communicates behind with the bony semicircu- 

 lar canals, and in front with the cochlea. Its outer 

 wall forms the inner wall of the tympanic cavity, 

 and in it is seen the fenestra ovalis, into which the 

 foot of the stapes is adjusted. The posterior part 

 of the vestibule receives five apertures that lead to 

 the semicircular canals, while its anterior part leads 

 by an elliptical opening into the scala vestibuli of the 

 cochlea. 



Superior semicircular canal. 



Horizontal semi- 

 circular canal. 

 Posterior semi- 

 circular canal. 



Ampulla. ^ ^mlGI*%- ^ny cochlea. 



Vestibule. Fenestra rotunda. 



Fig. 304. Right bony labyrinth, viewed from outer side: The figure 

 represents the appearance produced by removing the petrous portion of 

 the temporal bone down to the denser layer immediately surrounding 

 the labyrinth (from Quain, after Sommering). 



The utriculus and sacculus are two sac-like struc- 

 tures enclosed in the bony vestibule. The two are 

 indirectly connected by the ductus endolymphaticus , 

 which is a Y-shaped channel that terminates in a 

 blind recess, the saccus endolymphaticus. The latter 

 lies against the dura on the posterior surface of the 

 temporal bone. 



The utriculus is larger than the sacculus and occu- 



