CLASSIFICATION. 7 



Omitting mention of certain features connected with their osteolog}*, it may- 

 be observed that among those reptiles with four or five toes to each foot, while a 

 few, such as certain tortoises, have the same number of joints in each toe as 

 Mammals, — that is to say, two in the first toe, and three in each of the others, — in 

 the greater majority there is a departure from this simple arrangement. In the 

 lizards, for instance, the number of joints in the toes (reckoning from the first to 

 the fifth digit) is 2, 3, 4, 5, 3 in the fore-limb, and 2, 3, 4, 5, 4 in the hind-limb ; 

 while in crocodiles, where there are but four toes in the latter, the numbers are 

 respectively 2, 3, 4, 4, 3, and 2, 3, 4, 4. In this increasing number of joints in the 

 toes from the first to the fourth, such reptiles approximate to birds. 



As regards their soft internal parts, Reptiles are characterised by the low 

 development of their brains; which, in conjunction with their cold blood, accounts 

 for the generally sluggish movements of their existing representatives. With the 

 exception of the crocodiles, Reptiles differ from Birds in that the heart has only 

 three, in place of four, complete chambers, thus causing the freshly oxygenated 

 blood returning from the lungs to be mixed with the effete blood which has 

 traversed the body. Even in crocodiles, where the heart has practically four 

 chambers, the fresh and effete blood is partially mingled, owing to a communica- 

 tion between the vessels just outside the heart. Like Birds, Reptiles never have a 

 midriff completely separating the cavity of the chest from that of the abdomen. 



Classification Reptiles having come into existence at an earlier period than 



and Distribution. either Mammals or Birds, and attaining an enormous development 

 during epochs when both those groups were but feebly represented, it would be 

 only natural to expect that they should have suffered to a much greater extent by 

 the extinction of types with the lapse of time. As a matter of fact this is found 

 to be the case ; the number of existing orders of Reptiles being now but four (of 

 which one is represented by only one or two species), whereas, if we include the 

 extinct types, at least nine orders may be recognised. These nine orders, of which 

 the extinct ones are indicated by asterisks (*) may be named and arranged as 

 follows, viz. : — 



1 . Crocodiles — Crocodilia, 



*2. Dinosaurs — Dinosauria. 



*3. Flying Dragons — Ornithosauria. 



4. Tortoises and Turtles — Chelonia. 



*5. Plesk >saurians — Plesiosauria. 



6. Lizards and Snakes — Squamata. 



*7. Fish-Lizards — Ichthy osauria. 



8. Tuateras, or Beaked-Lizards — Rhynchocephalia. 



*i). Mammal-Like Reptiles — Anomodontia. 



Of these groups, by far the most numerously represented at the present day 

 is the one containing the lizards and snakes, all of which are highly specialised 

 forms, occupying a position in the class analogous to that held by the perching 

 birds in the preceding class ; the majority being comparatively small or medium- 

 sized forms. Next in point of numbers come the tortoises and turtles, all of which 

 are protected by the presence of a bony carapace, and some of which attain very 



