2360 



REPTILES 



In marked contrast to the uniformity in appearance and structure 

 characterizing Birds, the various groups of Reptiles differ widely from 

 Structure one another, both as regards external form and internal structure. Ex- 

 ternally, a lizard, a snake, and a tortoise present the most marked dif- 

 ferences in general appearance among living members of the order; while among 

 extinct types there were some which walked on their hind-limbs alone, after the 

 manner of Birds, and others having their fore-limbs modified into wings and the 

 digits connected by a leathery membrane like that of bats. In a typical Reptile, 

 such as a lizard or crocodile, both pairs of limbs are well developed, and of approxi- 



SKELETON OF FISH LIZARD OR ICHTHYOSAUR. 



mately equal length, but in the snakes all external traces of limbs have disappeared; 

 while in the extinct flying dragons, or Pterodactyles, the fore-limbs much exceed 

 the hind ones in size, and in many of the so-called Dinosaurs, which are likewise 

 extinct, the excess in size falls to the share of the hinder pair of limbs. In other 

 cases, again, the limbs may be modified into paddles, adapted for progression 

 in the water, as in the existing turtles, and the extinct fish lizards or Ich- , 

 thyosaurs; the body in the latter assuming a somewhat fish-like form. In nearly 

 all cases Reptiles have long and well-developed tails; although in some of the 



flying dragons these become 

 rudimentary. 



A large number of Rep- 

 tiles are characterized by the 

 development of bony plates 

 within the deep layer of the 

 skin; such plates, which are 

 well displayed in existing 

 crocodiles, being overlain by 

 horny shields, and thus 

 corresponding in every re- 

 spect with those forming 

 the carapaces of the arma- 

 dillos among Mammals. 



RESTORED SKELETON OF ARMORED DINOSAUR. 

 (About one-sixtieth natural size.) 



sc. shoulder blade or scapula; co. coracoid; h. upper arm bone or 

 humerus; r, u. bones of fore-arm or radius and ulna; c. wrist or carpus; 

 me. metacarpus; if. haunch bone or ilium; p. pubis; is. ischium; /. 

 thigh bone or femur; //', fi. bones of lower leg or tibia and fibula; fa. 

 ankle or tarsus; mt. metatarsus. After Marsh. 



Among certain extinct 

 Dinosaurs these bony plates 

 attain a development un- 

 paralleled at the present 



