96 THE EYE AND EAR. 
v. The inner nuclear layer: thick, and well stained. 
vi. The inner molecular layer; thick, but not stained. 
vii. The layer of nucleated nerve cells. 
viii. The layer of nerve fibres. 
ix. The internal limiting membrane. 
x. The radial fibres or Muller’s fibres: commencing 
with expanded ends in the ninth layer and 
stretching outwards: can easily be traced through 
the inner molecular layer. 
2. The choroid: spread a small prece of fresh choroid on a 
slide in normal salt solution: examine with low and high powers - 
note -— 
i, The network of bloodvessels: invested by 
ii, Pigment cells; irregularly branched: with clear 
nuclei. 
3. The lens; tease wn glycerine a small prece of lens hardened 
by boiling: examine with low and high powers: note :— 
i. The elongated cells of which the lens is composed. 
ii, The serrated edges of many of the cells. 
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 scessors 
and decaleify it by placing in a 5 to 10 per cent. solution of 
nitric acid, or 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 it from the decalcifying solution and 
transfer to weak alcohol and thence to strong alcohol. Then 
stain with borax carmine, imbed in paraffin, and cut into transverse 
sections with a microtome. Mount the sections in serves ; examine, 
and draw them showing :— 
1. The periotic capsule: consists mainly of cartilage, and is 
firmly fused with the hinder part of the cranium. 
