REPTILES 



375 



A harderian gland with a single duct is 

 always present; a naso-lacrimal duct never. The 

 lacrimal gland varies considerably. Curiously it 

 is large in marine turtles, and may be confined 

 to the temporal aspect of the orbit or scattered 

 along the length of the movable lower lid with 

 one or several ducts. 



The orbit of the turtle is relatively small 

 and enclosed ; some of the bones common to 

 the ^'ertebrates have been discarded, the nasal 

 and lacrimal bones, for examj^le. being replaced 

 by the frontal. 



Fig. 453. — The Poster- 

 ior Segment of the 

 Globe of the Turtle. 



L, tendon to lower lid ; 

 X, tendon to nictitans ; 

 P, pyramidalis niu.scle ; 

 R, retractor bulbi muscle 

 (after Franz). 



THE CROCODILIAN EYE 



THE CEOCODiLiA are the largest extant Reptiles, decadent survivors 

 of the giant Reptiles wliich dominated the earth in Mesozoic times. 

 Tliree genera are extant — the crocodiles, widely spread over tropical 

 rivers in Africa. Asia. Central America and Australia, the alligators 



ViG. 4.54.- 



-The Head of a young American Allig.ator of the Genus 

 Caimas (R. M. Holmes). 



of North and South America and Cliina, and the fish-eating ga vials 

 of the Ganges River. They are sluggish creatures, more motile on 

 water than on land where most of them obtain their prey, fond 

 of basking in the sun and prone to hide in mud in the hot season 

 (Fig. 454). Their eye?., primarily nocturnal in their characteristics, are 

 adapted for aerial vision for in their predominantly aquatic activities 

 these reptiles float with the eyes and nostrils above the surface and the 

 rest of the body awash. Their essential features are the ahseyice of scleral 

 ossicles, the reduced accommodative m.nscidature, the sUt-jmiiil, the 

 marked ciliary j^rocesses, the retinal taj^etum. the rod-rich retina, and the 

 rudimentary optic nerve. 



Gavial 



