488 



THE EYE IN EVOLUTION 



Figs. 643 to 645. — The Optic Nerve-head or Placentals. 



Fk;. 643. — The Optic Xerve-head of the Rabbit. 

 Note the absence of collagen fibres at the site of the lamina cribrosa 

 (Kolmer's fixative ; Azan ; X 27) (Katharine Tansley). 







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i 





^ ^ ^-'^ 







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Yw,. CiH. Tin: ( )i']i( Xerve-head op the Mouse. 



Note the band of evenly arranged oval nuclei running across the nerve 

 (Kolmer's fixative ; Feulgen ; x 369) (Katharine Tansley). 



Fig. 645. — The Optic Nerve-head of the 



Note the well-developed collagenous fibres at the lamina 

 fixati\o ; Azan : X 50) (Katharine Tansley). 



(Kolmer's 



