250 ELEMENTARY BIOLOGY. [XIIL 



& The molecular layer: this is thicker than any 

 of the preceding, and has a finely punctated ap- 

 pearance : running through it the fibres of 

 Miiller (h. 1 . i) are very plainly seen. 



. The inner granular layer: this is the layer 

 which usually looks clearest in sections, its ele- 

 ments being less closely packed than those of 

 the other layers. It is made up of a number 

 of nuclei (which in chromic-acid specimens look 

 granular), around which is collected a very small 

 amount of protoplasm, and of fine fibres, some 

 of which can be traced joining the nuclei or 

 granules. 



The inter-granular (fenestrated) layer. A narrow 

 cloudy layer in which no definite structural 

 elements are visible. 



77. The outer granular layer. Much thinner than 

 the inner granular layer and more closely 

 packed. It is composed of distinct fibres (rod- 

 and cone-fibres), each of which swells out and 

 has a nucleus (the granule) developed in the 

 enlargement. 



0. The external limiting membrane. A thin homo- 

 geneous layer like a. 



1. The fibres of Mutter. These are highly refract- 

 ing fibres which can be traced with ease from 

 the internal limiting membrane to the fenes- 

 trated layer. They probably run beyond the 

 latter and end on the external limiting mem- 

 brane, but are difficult to trace through the 

 outer granular layer. . 



