180 REPTILIA. 



Their lung extends more or less towards the posterior extremity 

 of the body; it frequently penetrates very far into the lower part of 

 the abdomen, whose transverse muscles pass under the ribs, and 

 even towards the neck, to clasp it. Those in which this organ is 

 very large, possess the singular faculty of changing the colours of 

 their skin according to the excitement produced in them by their 

 wants or passions. 



Their eggs are enveloped by a covering more or less hard, and 

 the young always retain the form in which they quit them. 



Their mouth is always armed with teeth, and their toes, with very 

 few exceptions, are furnished with nails; their skin is covered with 

 scales, more or less compact, or at least with scaly granules. They 

 all have a tail more or less long, and generally very thick at base; 

 most of them have four legs, a few only having but two. 



FAMILY I. 



CROCODILIDA. 



This family contains the single genus 



CROcoDiirs, Br. 

 Crocodiles are large animals, with a tail flattened on the sides, five toes be- 

 fore and four behind, of which only the three internal ones on each foot are 

 armed with nails, all more or less united by membranes; a single range of 

 pointed teeth in each jaw; the tongue fleshy, flat, and adhering close to its 

 edges; a circumstance which induced the ancients to believe that they had 

 none; the back and tiil covered with very stout, large, square scales or 

 plates, relieved by a ridge along their middle; a deeply notched crest on 

 the tail, which is double at its base. The plates on the belly are smooth, 

 thin, and square. Their nostrils, which open on the end of the muzzle by 

 two small crescent-shaped fissures closed by valves, communicate with the 

 extremity of the hind part of the mouth, by a narrow canal which traverses 

 the palatine and sphenoidal bones. 



The lower jaw being continued behind the cranium, the upper one ap- 

 pears to be movable, and has been so described by the ancients; it only 

 moves, however, with the entire head. 



They have the power of closing the external ear by means of two fleshy 

 lips, and there are three lids to their eyes. 



The vertebrae of the neck rest on each other through the medium of small 

 false ribs, which renders all lateral motion difiicult, and does not allow these 



