586 REPTILES. 



and Mammals; there are large lachrymal glands, but there is no special 

 deceitfulness about "crocodile's tears." 



The ears open by horizontal slits, over which lies a flap of skin ; three 

 Eustachian tubes — one median and one on each side— open into the 

 mouth behind the posterior nares. 



The nostrils also can be closed, and, as we have already noticed, their 

 internal opening lies at the back of the mouth. 



The stomach suggests a bird's gizzard, for it has strong muscular walls, 

 and its pyloric end is twisted upward so as to lie near the caidiac part. 



The heart is four-chambered, the septum between the ventricles being 

 complete, as in Birds and Mammals. But as the dorsal aorta is formed 

 from the union of a left aortic arch containing venous blood, and a right 

 aortic arch containing arterial blood, the blood which is driven to many 

 parts of the body is "mixed blood," i.e. blood partly venous, partly 

 arterial, with some of its red blood corpuscles carrying hsemoglobin and 

 others oxyheemoglobin. At the roots of the two aortic arches there is a 

 minute communication between them — the foramen Panizzse. 



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

 vense cavse 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 epigas- 

 trics 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 



