94 THE EAR 



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 rmth stout 

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

 of nitric acid, or in a niixtv/re of chromic acid with a few d/rops of 

 nitric acid. When the hones are thcyroughVy soft, which wiU take 

 from a few hours to Z or i: days or mm-e according to the strength 

 of add employed, remove the head from the decalcifying solution 

 tmd t/ransfer 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. Mownt the sections in 

 series ; examnine and, d/ravi 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 

 endolymph : 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 



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

 periotic cartilage and drawn from the outer surface. 



ffi, the anterior vertical semicircular canal ; b, its ampulla ; h, the 

 horizontal canal ; i, its ampulla ; p, the posterior vertical canal ; r, its 

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



