vra THE MEMBRANOUS LABYRINTH 393 



dilated at one of its two ends, where it opens into 

 the utricle, into what is called an ampulla (Fig. 123, 

 A, A, A), the other end having no ampulla. Thus 

 there is one ampulla to each canal. Those ends of the 

 two vertical canals which are not dilated into ampullae 

 join together (Fig. 124), before they open into the 

 utricle. 



On each ampulla is a ridge or crest, called crista 

 acustica, placed crosswise, and projecting into the 

 cavity of the canal. Each crest is formed partly by an 

 infolding and thickening of the connective tissue wall of 

 the ampulla, and partly by a thickening of the epithelium, 

 which here has the peculiar characters already referred 

 to. A similar but oval patch of thickened, modified, 

 auditory epithelium, with a thickening of the wall beneath 

 it, is found in the utricle itself ; this is called a 

 macula acustica. 



Attached to the utricule is a similar smaller sac (form- 

 ing another division of the primitive membranous bag) 

 called the saccule, on the walls of which is a similar 

 rounded patch of modified epithelium, or macula. The 

 cavity of the saccule is cut off from that of the utricle, 

 except for a curious roundabout connection by means of a 

 narrow canal (Fig. 124, A.V.). 



The utricle and saccule with the three semicircular 

 canals receive the name of the membranous laby- 

 rinth. It will be remembered that this membranous 

 labyrinth, filled with endolymph, lies in an intricate caAdty 

 with bony walls called the OSSeous labyrinth, of which 

 the part which contains the saccule and utricle is known 

 as the vestibule, and that between the walls of the 

 bony and the membranous labyrinth, which correspond 

 largely but not wholly in form, is a space filled with 

 perilymph. 



Branches of the auditory nei've pass to this mem- 

 branous labyrinth and send fibres (Fig. 124) to the three 



