94 THE EAH 



D. The Ear of the Frog. 



The frog's auditory organ is too small to dissect satisfactorily, 

 and is best studied by making transverse sections of the entire 

 head in the following manner : 



Kill a frog with chloroform; cut off the head with stout 

 scissors, and decalcify it by placing in a 5 to 10 per cent, solution 

 of nitric acid, or in a mixture of chromic acid with a few drops of 

 nitric acid. When the bones are thoroughly soft, which will take 

 from a few hours to 3 or 4 days or more according to the strength 

 of acid employed, remove the head from the decalcifying solution 

 and transfer to weak alcohol and thence to strong alcohol. Then 

 stain with borax carmine and imbed in paraffin, and cut into 

 transverse sections with a microtome. Mount tlie sections in 

 series ; examine and draw them, showing the following points : 



1. The periotic capsule consists mainly of cartilage, and is 



firmly fused with the hinder part of the cranium. 



2. The vestibule is a membranous sac lying in the cavity of 



the periotic capsule, and filled with a watery fluid, the 

 endolympli : it is partly divided by a constriction into 

 two main divisions : 



i. The utriculus is the upper and larger division, 

 ii. The sacculus is the inferior and smaller division : 

 from it arise three small saccular dilatations, 

 supposed to represent the cochlea of higher 

 animals. 

 iii. The ductus endolymphaticus rises from the inner 



FlG. 19. The right internal ear of the frog, removed from the 

 periotic cartilage and drawn from the outer surface. 



a. the anterior vertical semicircular canal; b, its ampulla; h, the 

 horizontal ca^al ; *', its ampulla ; p, the posterior vertical canal ; r, its 

 ampulla ; s, the sacculus ; u, the utriculus. 



