132 PRACTICAL HISTOLOGY. 



2. Layer of nerve fibres consists of the axial cylinders ot 

 the optic nerve fibres. 



3. Layer of nerve cells is composed of multipolar cells, 

 the central process of each being an undivided axial cylinder 

 process continuous with an optic nerve fibre, and the external 

 processes, several in number, dividing again and again, and 

 thus giving rise to smaller bundles of fibrils that pass out- 

 wards into the next layer, through which, however, they 

 have not as yet been traced. 



4. Inner granular layer ("inner molecular layer"). 

 With this magnifying power (300) it appears to be nothing 

 but minute granules, but when very highly magnified a clear 

 matrix containing fine granules may be seen. The fibres 

 of Miiller pass through it, and probably so do the nerve 

 fibrils. 



5. Inner n'uclear layer contains distinct nuclei, each with 

 a nucleolus. A few of them belong to the fibres of Miiller ; 

 the majority, however, belong to the nerve fibrils passing 

 outwards. (The nerve fibrils cannot be distinctly seen 

 without a much higher power.) 



6. Outer granular layer is much thinner, but is in other 

 respects similar to the inner granular layer ; its limits are 

 much more easily seen in a retina stained with carmine, 

 for then the inner and outer nuclear layers are stained, while 

 the granular layers are not. 



7 . Outer nuclear layer contains many nuclei, the majority 

 of which belong to the rod nerve fibrils, one nucleus upon 

 each fibril placed at various parts of their course. The 

 fibrils, however, can only be seen with a very high power, 

 and best in the osmic acid retina. Transverse striation 

 of these nuclei first pointed out by Henle is very evident ; 

 the general substance of the nucleus is highly refractile, 

 and is crossed by one, sometimes two stripes of a less 

 refractile substance. There is no nucleolus. It is much 

 more difficult to find the single nucleus with nucleolus upon 

 the cone fibre placed just within the outer limiting membrane. 

 It has no stripes, and is exactly like the nuclei of the inner 

 nuclear layer. It is best seen in the osmic acid retina of 

 the frog. 



