REPTILES 



dotted with melanophores, and in a few instances these form a contin- 

 uous thin layer of dense pigment (Lichanura, Sonora, Abastor, Farancia, 

 Ndtrix, Acanthophis) . In Python (molurus) there are also many flat 

 pigment cells at various levels in the scleral tissue itself. 



Fig. 181 — The ophidian eye in vertical section: Natrix natrix. x22. 

 Redrawn from Schwarz-Karsten, modified from original preparations. 



am- accommodatory muscle; ap- anterior pad of lens; b- brain; c- cornea; cb- ciliary body 

 (main portion, the ciliary roll; note cross-section of hyaloid vein lying on orbiculus behind 

 it; the very small vessels of the hyaloid plexus, lying on the inner surface of the retina, are 

 omitted from the drawing); cr- cranium; cs- canal of Schlemm; hg- Harderian gland; io- 

 infraocular scale; s- sclera; sm- sphinaer muscle; so- supraocular scale; sp- spectacle; ^- 

 zonule (collapsed; see text). 



The cornea is strongly arched and of almost uniform thickness except 

 — usually — toward its margin, where it is markedly thickened (the 

 'corneal thickening' hereinafter mentioned). This thickening is lacking 

 in many small eyes with thin scleras (e.g., Charina, Phyllorhynchus, 

 Hypsiglena, Trimorpbodon) , and even in the presence of a relatively 

 thick sclera, as in Tropidopbis (where the peripheral zone of the cornea 

 is actually thinned) and Eryx. 



