REPTILES 



381 



pattern comprises a system of arcades running towards the pupillary- 

 margin, some of the vascular loops of which leave the iris and float 

 freely in the anterior chamber (Mann, 1931) (Figs. 461 and 462). 

 The round jpwpil contracts into a vertical slit, and both circumferential 

 sphincter and radial dilatator muscle fibres are present. 



The lens is large, making the anterior chamber shallow ; it is 

 more spherical than in diurnal lizards and the annular pad is well 

 developed. The zonular fibres are peculiar in that, arising from the 



Figs. 461 and 462. — The Iris of Sphexodox. 



Fig. 461. — Showing the vascular arrangements (Ida Mann). 



Fig. 462. — Showing the pigmentary epithehum, ^4, tlie sphincter mu-scle, 

 C, and the peciihar vascular arrangements. Among the.se, B is an afferent 

 vessel from the ciliary region, and D is one of the many arteries of the iris 

 which float freely in the anterior chamber. £' is a nerve trunk (Ida Mann). 



ciliary body, they are inserted into the posterior surface of the iris as 

 well as into the lens, as if the former tissue were imjjressed into the act 

 of accommodation by being forced against the periphery of the lens 

 to make the axial area bulge forward.^ 



The retina has received a considerable amount of study. ^ It is 

 completely avascular and a conus is absent ; only a few capillaries are 

 evident forming a network on the pale vertically elongated optic disc, 

 to which structure they are rigidly restricted (Plate VIII). Ophthal- 



1 p. 651. 



2 Osawa (1898-99), Kallius (1898), Virchow (1901), Bage (1912), Mann (1932-33), 

 Walls and Judd (1933), Walls (1934). 



