CROCODILES. 



CROCODILE OF THE NILE. 



FAMILY OF CROCODILIANS. 



9. Crocodiles differ in so many respects from other Saurians, 

 that many authors think they ought to constitute a separate 



f JQ order. Their internal 



organization seems to 

 place them as a con- 

 necting link between 

 reptiles and the higher 

 vertebrata. They are 

 very easily recognised 

 by their laterally com- 

 pressed tail, and by their 

 toes, five before, and four behind, all of them more or less united 

 by membranes, which is indicative of aquatic habits. 



10. The most remarkable peculiarity in the structure of these 

 animals, is the disposition of their circulatory system : it is such 

 that the whole posterior part of the body receives only a mixture 

 of arterial and venous blood, while the head is supplied with pure 

 arterial blood. The heart has four cavities, two auricles, and 

 two distinct ventricles, as in mammals and birds. The arterial 



blood, coming from the lungs, passes 

 from the left auricle into the ventricle 

 of the same side, which in its turn, sends 

 the blood into the aorta, (Fig. 11.) The 

 [.. a p venous blood, received into the right ven- 

 tricle, finds no direct passage into the 

 left ventricle, as is the case in other rep- 

 tiles ; but it does not all go to the lungs, 

 as it does in the warm-blooded verte- 

 brata ; for, alongside of the pulmonary 

 arteries, (op.) is found another vessel, 

 (a.) which also arises from the right ven- 

 tricle, and which, after bending back- 

 wards behind the heart, terminates in the 



Explanation of Fig. 11. Heart and great vessels of a crocodile: 

 t?, t), veins which bring the blood from different parts of the body to the right 

 auricle of the'heart, (od,) w, the two ventricles which are separated inter- 

 nally by a paitition, ap, the two pulmonary arteries which go from the 

 right ventricle to the lungs, a, the vessel which arises from the same ven- 

 tricle, and empties into the descending aorta, vp, pulmonary veins which 

 convey the arterial blood from the lungs to the left auricle, (og,} from which 

 it descends into the left ventricle, and directly enters the aorta, (ao,) and the 

 two arteries, (c, c,) which are distributed to the head, &c. 



9. What are the general characters of the crocodiles ? 

 10. What are the peculiarities in the circulation in crocodiles ? 



Fig. 11. 

 ap c c a 



vp 



