188 



THE FROG 



CHAP. 



is directed outwards and has a horizontal position. 

 Each canal has one end dilated into a bulb-like swelling 

 or ampulla (am] ; those of the anterior and external 

 canals are at their anterior ends, while that of the pos- 

 terior canal is at its posterior end. 



The whole of this apparatus is filled with a fluid, the 

 endolymph, in which are contained calcareous particles, 

 the otoliths or ear-stones. It is made of connective- 



FIG. 60. Longitudinal section through an ampulla. 



:. e. auditory epithelium ; a. h. auditory hairs ; c. part of semicircular canal ; c. r. 



acoustic spot and ridge ; c. t. connective-tissue ; e. epithelium ; n. nerve ; 



M. junction with utriculus. (From Foster and Shore's Physiology.) 



tissue and lined with epithelium, the cells of which are 

 cubical for the most part ; but in certain places the wall 

 is thickened, forming what are called acoustic spots, of 

 which there is one to each ampulla, situated on a ridge 

 (Fig. 60), while others occur in the utriculus and sac- 

 culus. On these acoustic spots the epithelial cells are 

 greatly elongated, and produced at the surface intc 

 delicate processes called auditory hairs : to these cell: 

 the fibres of the auditory nerve are distributed. 



