542 GENERAL CHARACTERS OF REPTILES. 



skeleton; the mouth destitute of teeth, but furnished with a 

 horny beak ; the skin covered with large horny plates ; and the 

 members, four in number, all formed upon the same plan. 



II. LORICATA, or Crocodiles; Lizard-like Reptiles, with the 

 skin covered with bony plates ; toothed jaws ; four complete 

 members; and the external aperture of the cloaca forming a 

 longitudinal slit. 



III. SAURIA, or Lizards; in which the dorsal vertebrae and 

 ribs are movable, so that there is neither carapace nor plastron ; 

 the jaws are toothed, and the tympanic bone fixed; the skin is 

 covered with horny scales and the cloacal aperture is transverse. 

 Limbs usually four. 



IV. OPHIDIA, or Serpents; which are formed upon the same 

 general plan as the Lizards, but have the tympanic bone mov- 

 able, and are always destitute of limbs. 



As the chief peculiarities of these several orders have been 

 already noticed, a very short account of some of the principal 

 families included in them will suffice. 



ORDER I. CHELONIA. 



483. The animals composing this order vary considerably in 

 those details of their structure, which adapt them to different 

 habits of life ; some of them being destined to reside exclusively 

 upon the solid ground, others to pass nearly their whole time in 

 water, and others to dwell amidst marshes, the muddy banks 

 of rivers, &c. The most obvious variations are in the structure 

 of the feet, and in the form of the shell. Thus in the proper 

 Land- Tortoises, we meet with a short stumpy foot, not unlike 

 that of an Elephant, the toes not being separated, and only the 

 claws apparent (Fig. 316.) In the Marsh and River- Tortoises, 

 the toes are divided and webbed, so as to increase the extent of 

 surface ; and in the Marine- Tortoises, or Turtles, we find them 

 extended into large undivided paddles, by which the animals 

 can propel themselves rapidly through the water (Fig. 318). 



