40 ORGANIZATION OF SAURIANS. 



2. Their extremities are short, and placed unfavourably for 

 rapid movement. In general, they are wide apart, and directed 

 outwards at a right angle with the body, so that they cannot 



sustain the weight of the trunk : most of these reptiles drag the 

 belly and tail on the ground. The toes, which are very distinct, 

 and ordinarily five in number, terminate in sharp, curved nails ; 

 sometimes they are very long and slender, at others, widened, 

 and furnished beneath with folds variously arranged, and at other 

 times again, united by palmate membranes, which modifications 

 are in conformity with the animal's mode of life. 



3. The skeleton has no important remarkable peculiarity. The 

 number of vertebrae is very variable, particularly in the caudal 

 region : there always exist moveable ribs which often protect the 

 abdomen as well as the thorax. The sternum is never wanting. 

 The shoulder is ordinarily formed of three bones, (a scapula, a 

 clavicle, and a coracoid bone,) united in a kind of ring, so as to 

 envelope the anterior part of the chest, and all concur in the 

 formation of the cavity designed to lodge the head of the humerus. 

 The pelvis is also composed of three pieces, and is joined to the 

 sacrum, which consists of two vertebrae. 



4. The skin of these animals is always covered by a thick and 

 unequal epidermic layer, which forms scales or plates of greater 

 or less size. 



5. The mouth, which is deeply cleft, is without fleshy lips ; it 

 is armed with teeth, generally of a conical form, that serve to 

 seize and hold their prey, but rarely to grind their food. They 

 are often found in the palate, as well as in the two jaws. The 

 food of Saurians consists essentially of animal substances ; the 

 digestive canal is ordinarily quite short ; in general, the stomach 

 is scarcely distinguishable from the oesophagus ; but sometimes 

 it has the form of a more or less globular pouch. 



6. The disposition of the circulatory system, varies in these 

 animals ; in general, the heart is but imperfectly divided in its 

 ventricular portion, so that the venous blood and arterial blood 

 mingle in its interior; but in crocodiles, the separation between 

 the two halves of this organ is complete, and the mixture of the 

 two kinds of blood takes place only in the descending aorta. 



7. The lungs, in general, are large, and extend more or less 

 into the abdomen. The air is renewed in them by the same 



2. What is the character of their extremities? 



3. What is nmarkablc in the skeleton of Sauria? 



4. What is the character of the skin of Sunria ? 



5. What is the character and situation of thr teeth in Siuria ? 



6. Is the circulation of the blood the same in all Sauria? What are ita 

 general characters ? 



7. How do the Saurian'*, breathe ? 



