i88 



THE FROG 



external canal {ce), is directed outwards and has a hori- 

 zontal position. Each canal has one end dilated into 

 a bulb-like swelling or ampulla (aa, ap, ae) ; those of 

 the anterior and external canals are anterior in position, 

 while that of the posterior canal is posterior. 



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 tissue and 



Fig. 60. — Longitudinal section" through an ampulla. 

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

 acoustic spot and ridge ; ct. connective tissue ; e. epithelium ; n. nerve ; 

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



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 sacculus. On these acoustic 

 spots the epithelial cells are greatly elongated and produced 

 at the surface into delicate processes called auditory hairs': 

 to these cells the fibres of the auditory nerve are distributed. 



