624 REPTILES 



thus directly squeezed equatorially when the ciliary muscle contracts 

 and moves the anterior end of the ciliary body forward and axiad (see 

 Fig. 109, p. 275, and Fig. 182, p. 632). 



The ciliary muscles show great variations from lizard to lizard. Typ- 

 ically, perhaps, they are as described on pp. 277-80; but they are often 

 much simpler. In the Teiidse, for example, the muscle is all in one piece, 

 its purely meridional fibers originating from the corneal margin iv.s.) 

 and terminating in the base-plate and on the glass membrane. In noc- 

 turnal forms, the muscle may be massive or it may be greatly atrophied 

 as if the animal had abandoned all attempts to accommodate. The 

 muscle is tiny in Xantusia riversiana and in Hem'tdactylus mabouia, and 

 absent in X. henshawi, X. vigilis, and Heloderma siispectum. It is huge 

 in Coleonyx variegatus, however, and is well developed in Aniella pul- 

 chra considering the size of the eye. There are often special arrangements 

 which seem purposed to produce a nasad shift of the lens during accom- 

 modation, thus aiding the transversalis muscle (usually present) in 

 converging the visual axes. Thus in Seps and Lacerta, bundles of circum- 

 ferential fibers have been described and figured in the temporal half of 

 the eye (cf. Sphenodon) ; and in Tupinambis, though all the fibers are 

 meridional, they are much longer on the temporal side. 



The iris is relatively thick, and often thicker toward the pupil, where 

 there is a vascular plexus fed by a temporal and an inferior artery and 

 drained by many radial veins. The sphincter is scattered through the 

 whole iris, and some of its fibers are bowed into radial positions and 

 must act separately, since no other dilatator is present. Where the pupil 

 is a vertical slit, the arrangement may be very complicated (see Fig. 88e, 

 p. 223). Both retinal layers are deeply pigmented. The zonule is very 

 thick where it attaches to the lens, and its anteriormost laminae run 

 parallel to the iris and so close to it that they suggest the origin of 

 the 'bridge-membrane' of Sphenodon. 



The lens has an extremely thin capsule and is very soft, though not 

 so much so as in turtles. Its 'ringwulst' or annular pad is relatively thick 

 — in the chameleons, the thickest known. In the diurnal majority the lens 

 is flatter than in any other reptiles. The primary vitreous forms a broad 

 funnel, indicating that the slender hyaloid canal seen in turtles — though 

 these are the most primitive of living reptiles — is something special. 



Pointing through the watery vitreous toward the heart of the lens is 

 the conus papillaris, a slender papilla rooted on the ventro-temporal optic 

 nerve head (Fig. 182, p. 632). It consists largely of tiny blood vessels 



