•250 THE VITAL FUNCTIONS. 



The heart of the Cheloiiian reptiles, such as the 

 ordinary species of Tortoises and Turtles, has two 

 distinct auricles ; the one, receiving the blood from 

 the pulmonary veins ; the other, from those of the 

 body generally ; so that the aerated and vitiated 

 blood are poured together, and partially mixed in 

 the ventricle, the cavity of which is, to a certain 

 extent, divided into two chambers by an imperfect 

 partition. This conformation has the etiect of 

 directing the more oxygenised portion of the blood 

 to the head and limbs, and the more carbonised 

 portion to the digestive and other abdominal organs; 

 while the blood sent to the lungs is almost entirely 

 of a venous quality. When all the cavities are 

 distended with blood, the two auricles being nearly 

 of the same size as the ventricle, the whole has the 

 appearance of a union of three hearts. The circu- 

 latory system of the Ophidia is constructed on a 

 plan very similar to that of the Chelonia. 



In the Saurian reptiles, the structure becomes 

 again more complicated. In the Chameleon each 

 auricle of the heart has a large venous sinus; the 

 two appearing like supplementary auricles.* The 

 heart of the Crocodile has a ventricle divided, by 

 two partitions, into a right, a middle, and a left 

 chamber : from the first proceeds the right aorta ; 

 from the second, the pulmonary artery; and from 

 the third, the left aorta. The partition which is 

 interposed between the right and the middle cham- 

 ber is very imperfect, and allows of free communi- 

 cation between these chambers ; so that the venous 

 blood poured into them from the right auricle is 

 divided between the right, or visceral aorta, and the 



* Houston; Trans. Roy. Irish Acad, xv, 189. 



