CROCODILES. 43 



descending aorta, (ao.) It follows, therefore, that at every con- 

 traction of the heart, one portion of venous blood is sent to the 

 lungs, and another portion is mingled with the arterial blood ; 

 but this mixture takes place in the interior of the aorta, below 

 the point of origin of those branches, (c,c.J which this vessel 

 sends to the head and anterior part of the trunk, so that these 

 parts receive pure arterial blood, while all those, the arteries of 

 which arise posteriorly to the point of junction between the aorta 

 and the vessel coming from the right ventricle, receive only a 

 mixture of red and black blood. 



11. The lungs of Crocodiles do not extend into the abdomen, 

 like those of other reptiles, and are separated from its viscera by 

 a sort of imperfect diaphragm. It is also to be remarked, that 

 the canal through which the air penetrates to these organs, can 

 be completely separated from the mouth by letting down a fold, 

 analogous to the veil of the palate in mammals, an arrangement, 

 which permits them to remain under water, with the mouth open, 

 to await their prey, without interrupting their respiration. And 

 their nostrils, which open at the extremity of the muzzle, are 

 closed by valves. 



12* Their mouth is cleft beyond the ears, and the lower jaw is 

 prolonged backwards beyond the cranium, which makes the upper 

 one seem to be moveable ; but it only moves with the cranium. 

 There is, in each jaw, a single row of very strong, pointed teeth, 

 planted in distinct alveoli. The tongue is fleshy, flat, and attached 

 to the lower jaw, very close to its edges, and hardly distinct from 

 it, which led the ancients to believe that it was entirely wanting. 

 The stomach is in the form of a rounded pouch. 



13. The skeleton also, has several peculiarities. The cervical 

 vertebrae rest one on the other through the medium of small 

 false ribs, which renders lateral motion difficult. Besides the 

 ordinary ribs, there is found, between the muscles of the abdo- 

 men, analogous bones, which protect the viscera without extend- 

 ing to the dorsal spine ; these reptiles are the only Saurians that 

 want clavicles, properly so called. 



14. Crocodiles are large animals; their back is covered by 

 large, square, very strong scales which are carenate (ridged,) in 

 the middle. The tail has a similar covering, and is furnished on 

 top with a strongly notched crest which is double at its base ; the 



11. What are the peculiarities of the respiratory organs in Crocodiles? 



12. Do Crocodiles move the upper jaw ? What is remarkable in the lower 

 jaw ? What is the character of their teeth ? Have Crocodiles a tongue ? 

 What are its peculiarities ? 



13. What are the peculiarities of the skeleton ? 



14. What is the character of the integuments of Crocodiles ? 



