XIX] 



SENSE-ORGANS 



423 



cones , () the outer nuclear layer (vi, Fig.. 212) consisting of the 

 bodies ot the visual cells containing their nuclei; (c) the outer 

 molecular layer (v, Fig. 212) consisting of sections of the hasal 

 processes of the visual cells and of the receptive dendrites of the 

 neurons with small cell bodies ; (d) the inner nuclear layer (iv, Fig. 

 212) consisting of the bodies of the above neurons; (e) the inner 

 molecular layer (in, Fig. 212) consisting of sections of the basal 

 processes of the above neurons and of the receptive dendrites of the 



FIG. 212. Diagram to illustrate structure of a retina. The several "layers" 

 are indicated by the numerals in, etc. in order from within (vitreous 

 humour) outwards. 



3. Nucleus of rod-cell. 

 Pigment epithelium. 



7. 



4. Small neuron. 

 Fibre of Muller or 



1. Cone. 2. Eod. 



5. Large neuron. 

 a supporting cell. 



neurons with large cell bodies ; (/) the layer of nerve-cells consisting 

 of the bodies of the last-named neurons ; and finally (g) the layer 

 of nerve-fibres consisting of the basal processes of the last-named 

 neurons which constitute the optic nerve. 



The remainder of the eye is to be looked on as a part of the 

 skin of the side of the head which has been rendered transparent 

 in order to allow light to reach the retina. It consists of a lens 

 and cornea, separated by a chamber containing the aqueous 

 humour. The lens is an originally hollow plug of ectoderm cells, 



