4 REPTILES. 



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 approximately 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 progres- 



SKELETON OF FISH-LIZARD, OR ICHTHYOSAUR. 



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

 Ichthyosaurs ; 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 be- 

 come rudimentary. 



A large number of Rep- 

 tiles are characterised 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 arm- 

 adilloes among Mammals. 



RESTORED SKELETON OF ARMOURED DINOSAUR (about ^ Hat. size). 



sc, shoulder-blade, or scapula; co, coracoid ; h, upper arm-bone, or Among Certain extinct 



humerus ; r, u, bones of fore-arm, or radius and ulna ; c, wrist or carpus ; Dinosaurs these bony plates 

 me, metacarpus ; il, haunch-bone, or ilium ; p, pubis ; is, ischiurn ; /, . , , 



thigh-bone, or femur ; ti,fi, bones of lower leg, or tibia and fibula ; ta, attain a development Un- 



ankle, or tarsus ; mt, metatarsus. After Marsh. paralleled at the present 



day ; and in some they are 



believed to have occupied the extraordinary position shown in the accompanying 

 figure. 



Still more remarkable differences exist with regard to the form and structure 

 of the teeth; which, instead of being, as in the two preceding classes, strictly 

 confined to the borders of the jaws, may be spread over the entire palate. 

 In spite, however, of this diversity of form, the teeth of Reptiles differ from many 

 of those of the majority of Mammals in that they are never implanted in the 



