DIFFERENTIATION OF RETINAL ELEMENTS 49 



region of the posterior pole. The migration of cells from the 

 primitive nuclear layer into the marginal layer produces an 

 inner cell layer (Figure 33, B). Thus the original layer of 

 cells becomes divided into an inner and an outer neuroblastic 

 1st STAGE 2nd STAGE 3rd STAGE ADULT 



4-5 week 



6th week -3rd month 3rd -7th month 



Surface of marginal 

 layer 



- Internal limit- 

 ing membrane 



Marginal 

 layer 



Primitive 



neuro- 

 epithelium 



Basement 

 membrane 



Superficial 



portion of 



marginal layer 



Inner neuro-' 

 blastic layer " 



Transient non- 

 nucleated layer 

 of Chievitz 



Outer neuro- 

 blastic layer 



^- Nerve fiber 



layer 



;^ Ganglion cells - 

 ■:>-Amacrine cells 



Miillerian 



fiber 



nuclei 



Bipolar cells 



Horizontal 

 cells 



Nuclei of rods 

 and cones 



■^- Nerve fiber 

 layer 



■^- Ganglion cells 



Inner molecular 

 layer 



Inner nuclear 

 layer 



Outer molecular 

 layer 



Outer nuclear 

 layer 



Cilia • 



■^- Cilia 



Primitive rods 

 and cones — 



■>- External Hmit- 

 ing membrane 



->-Rods and cones 



Outer wall of 

 optic cup — 



^ >- Pigment 



epithelium 



layer with an intervening narrow zone devoid of nuclei 

 (transient non-nuclear layer of Chievitz). From these two 

 neuroblastic layers the retina is constructed by further 

 proliferation and differentiation, which proceeds from within 

 outward. The ganglion cells are the first of the retinal ele- 

 ments to appear, the rods and cones the last. 



