MAMMALS 



435 



ciliary iveb of Walls. 1942) — a mammalian characteristic (Fig. 542). As 

 in SaurojDsida generally, the connective tissue of the ciliary region runs 

 forwards to be inserted into Descemets membrane and embedded in 

 this lies the ciliary venous sinus, a structure more pronounced in 

 Placentals ^ (Fig. 543). The brown iris is tenuous, consisting merely of 



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, 3 



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Fig. 545. — The Retina of the Platypus. 



1, optic nerve fibre layer ; 2, ganglion cells ; 3, inner plexiforni laj-er ; 

 4, inner nuclear laj'er ; 5, outer plexiforni layer ; 6, outer nuclear layer ; 

 7. external limiting membrane ; 8, visual cells ; 9, jaigmentarv epithelium ; 

 10, choroid (O'Day). 



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Fig. 546. — The Retina of the Echidna. 



1, optic nerve fibre layer ; 2, ganglion cells ; 3, inner j^Iexiforni laj'er ; 

 4, inner nuclear layer ; 5, outer plexiforni layer ; 6, outer nuclear layer ; 

 7, external limiting membrane ; 8, visual cells (O'Day). 



1 p. 472. 



