114 



PHYSIOLOGY 



CHAP. 



almost exactly along the three dimensions of space. The two 

 vertical canals on each side unite together in their posterior 

 part, so that in the utricle there are five instead of six openings 

 to the canals, as shown in Fig. 45. 



Each canal is dilated at one end into a swelling or ampulla, 

 in which a branch of the vestibular nerve ends in the crista 

 acustica, which rises almost to the axis of the canal, and is clothed 

 with special sensory cylindrical cells. These cells of the sensory 



cnp.ttrn* 



Fio. 48. Longitudinal seeticm of ampulla of a fish, taken through the crista acustica. Diagram- 

 matic. (B. A. Schafer.) amp., cavity of the ampulla ; sc.c., semicircular canal opening out of 

 it; c., connective tissue attached to wall of the membranous ampulla and traversing the 

 perilymph ;., e., flattened epithelium of ampulla ; h., auditory -hairs projecting from columnar 

 cells of auditory epithelium into the cupola, cup. term. ; v., limit of the auditory epithelium 

 on the crista ; n., nerve-fibres entering base of crista, and passing into the columnar cells. 



epithelium carry long flexible hairs, which are thicker than those 

 of ordinary ciliated epithelium, and are held together by a 

 mucous, gelatinous mass so that they are unable to move freely 

 in the endolymph (Fig. 48). 



The nerve end-organs of the utricle and saccule are very 

 similar to those of the ampullae. These special sense-organs, 

 known as the macula acustica, are formed by the endings of twigs 

 of the vestibular nerve (Fig. 49). The remainder of the wall 

 of both utricle and saccule is destitute of nerves. 



The sensory epithelium of the macula has shorter hairs than 



