694 THE EAR 



project from the posterodorsal aspect of the vestibule; at the other end 

 the bony cochlea containing its series of spiral canals projects anteriorly 

 from the vestibule. Collectively these spaces, with several diverticula, 

 form the bony labyrinth, and within them in life are contained a num- 

 ber of membranous sacs whose general form corresponds more or less 



FIG. 578. THE BONY LABYRINTH. 



1, round window; 2, osseous lamina spiralis; 3, osseous cochlear canal; 4, floor of 

 internal acoustic meatus; 5, vestibule; 6, 7, 8, 9, semicircular canals. The figures 

 are placed at that portion of the margin which is nearest the structure indicated. 

 (After Rudinger.) 



closely to that of the bony cavity; these sacs collectively form the mem- 

 branous labyrinth. 



The vestibule contains two of these membranous sacs, the sacculus 

 and the utriculus, which are connected by means of the slender utriculo- 

 saccular canal, from which a much prolonged diverticulum enters the 

 aqueductus vestibuli to penetrate to the posterior surface of the petrous 

 bone where it comes into relation with the cerebral meninges ; this di- 

 verticulum is known as the ductus endolymphaticus. Its dilated terminal 

 portion constitutes the endolymphatic sac, which lies upon the dura and 

 probably opens into the subdural space. The utricle and saccule, as also 

 all other portions of the membranous labyrinth, contain a watery fluid, 



