386 



THE EYE IN EVOLUTION 



epithelium caps a ])ad of highly vascular, deejjly pigmented uveal 

 tissue (Fig. 470) ; from this ciliary roll strands of fibrous tissue 

 run forwards across the angle of the anterior chamber to find insertion 

 in the peripheral corneal thickening. The circumferential ciliary 

 venous sinus is usually corneal in location separated from the anterior 

 chamber by connective tissue and draining backwards into the uveal 

 veins of the ciliary region (Fig. 472). Individual variations, however. 



Fig. 470. — The Anterior Se(3ment of the Eye of the Tiger Snake. 



Externally is the sjDectacIe, s, beneath which the cornea, c, is seen with 

 the peculiar thickening at its limbal margin. Between s and c lies the closed 

 conjunctival sac. I, lens. The ciliary roll, cr, is a marked feature and above 

 it is seen the ]ioctinate ligament traversing the angle of the anterior chamber 

 immediately above which is the large ciliary venous sinus within the corneal 

 limbus ( X 53) (Norman Ashton). 



C'ohra 



occur particularly among the Boidae ; in Python, for example, it is 

 situated close to the outer surface of the cornea and drains into the 

 sulK-onjunctival veins, and in Constrictor- and the sand-boa, Eryx, 

 it is absent. 



The iris is a thick and relatively massive tissue heavily pigmented 

 vvith melanophores, lipojahores and iridocytes. As a rule, however, the 

 resultant colour-scheme is relatively dull and compared with many 

 other Rej)tiles the variations are small, the jDreponderant colours being 

 browns and yellows sometimes with a metallic sheen ; quite often the 

 colour-pattern of the skin is continued in the eye (Plate IX). 



Thus in the cobras (Elapid;e) the iris is brownish-yellow speckled with gold ; 

 ill the corn-snake, Coluber guttatus, orange-red ; in Python, brown with a metallic 



