OPTIC 

 SICLE 



Fig. 100. The origin and 

 early development of the eyes. 

 Top: The optic vesicles grow 

 out laterally from the fore- 

 brain. The connection between 

 the optic vesicle and the brain 

 is the optic stalk. Center: The 

 left eye cup shows a thick 

 nervous layer and a thin pig- 

 ment layer. The lens and cor- 

 nea are differentiating. The 

 right eye shows choroid fis- 

 sure and nerve cell sending 

 out nerve fiber through optic 

 stalk. Bottom: Relationship 

 between the nerve cells and 

 the photoreceptor cells within 

 the retina. The photoreceptors 

 are behind the nerve cells, 

 and light passes through the 

 latter before it strikes the re- 

 ceptors. 



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