640 REPTILIA. 



Into the right auricle venous blood is brought by the two superior 

 venae cavae and by the inferior vena cava. The blood passes through 

 a valved aperture into the right ventricle, and is driven thence (a) by 

 the pulmonary artery to either lung, or (b) by the left aortic arch to 

 the body. From this left aortic arch, before it unites with its fellow 

 on the right to form the dorsal aorta, is given off the great cceliac 

 artery. The anterior viscera thus receive wholly venous blood from 

 the heart. 



The blood driven to the lungs is purified there, and returns by pul- 

 monary veins to the left auricle. Thence it passes through a valved 

 aperture into the left ventricle. Thence it is driven into the right aortic 

 arch. From this the carotids to the head and the subclavians to the 

 fore-limbs are given off. These parts of the body thus receive wholly 

 arterial blood from the heart. 



The venous blood returning from the posterior regions may pass 

 through the kidneys in a renal -portal system, and thence into the 

 inferior vena cava ; or it may pass through the liver in a hepatic-portal 

 system, and thence by hepatic veins into the inferior vena cava ; or some 

 of it may pass directly into the inferior vena cava. The renal-portal 

 veins arise from a transverse vessel uniting the two branches of the 

 caudal, but the latter are also continued forward as lateral epigastrics 

 which enter the liver. 



The temperature of the blood is not above that of the surrounding 

 medium. 



In regard to the respiratory system, we should notice that the lungs 

 are invested by pleural sacs, as is the case in Mammals. 



The ureters of the kidneys, the vasa deferentia from the testes in the 

 male, the oviducts from the ovaries in the female, open into the cloaca, 

 which has a longitudinal opening. The penis is on the anterior surface 

 of the cloaca. 



The eggs, which in size are like those of geese, have a thin calcareous 

 shell, are buried in excavated hollows, and, warmed by the sun, hatch 

 without incubation. 



Of one species of crocodile it is known that the mother opens up the 

 nest when the young, ready to be hatched, are heard to cry from 

 within the eggs. The mothers take some care of the young, which 

 require to be defended even from the appetite of the males. 



Crocodiles are relatively sluggish, and fond of basking passively, 

 sometimes hiding in the mud during the hot season. They are remark- 

 able for the long continuance of growth, which does not seem to have 

 so definite a limit as in most other animals. 



Classification of Crocodilia 



(a) The true Crocodiles, of the genus Crocodilus, occur in Africa, 

 Southern Asia, tropical Australia, Central America, and the West 

 Indies. 



The Indian crocodile (C. porosus] may measure about 18 ft. in 

 length, and even larger forms have been recorded. The sacred African 



