250 ELEMENTARY BIOLOGY. [XIII. 



B. 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. ] . i) are very plainly seen. 



6. 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. 



f The inter-granular {fenestrated)layer. A narrow 

 cloudy layer in which no definite structural 

 elements are visible. 



7]. Tlie 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. 



w- d. The external limiting membrane. A thin homo- 

 geneous layer like a. 



i. The fibres of Miiller. 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. 



