COLD-BLOODED VERTEBRATA 391 



septum into right and left chambers, except in crocodiles, 

 where the division is complete, so that there are two 

 ventricles as in birds and mammals. There is no conus 

 arteriosus, and the pulmonary artery and right and left 

 systemic arches communicate with the ventricle each by an 

 opening of its own, though the systemics may adhere 

 outwardly to form a so-called truncus arteriosus. They 

 cross at their bases, and in crocodiles the right arch arises 

 from the left ventricle and the left arch, with the pulmonary, 

 from the right ventricle. The right is the more important 

 channel of the two, and conveys the arterial blood. These 

 dispositions foreshadow that of the birds, in which the right 

 systemic arch alone persists. (The only complete aortic 

 arch of a mammal is the left systemic.) In most lizards 

 (Fig. 415) the ductus Botalli persists, and in turtles the 

 ductus arteriosus. The venous system of a reptile is much 

 like that of an amphibian, and has a renal portal system, 

 which is lacking in birds and mammals. The red blood 

 corpuscles are oval and nucleated, like those of other cold- 

 blooded vertebrates and birds, not like those of mammals. 

 Turtles, whose ribs are fixed by their shell (p. 393), breathe 

 like Amphibia by forcing air into the lungs from the mouth, 

 other reptiles breathe like mammals by drawing air into the 

 lungs, but this is done by the movement of the ribs only, 

 since there is no midriff. (The active movement in the 

 breathing of a bird is that by which the air is driven out.) 

 There is no important difference between the reptilian and 

 amphibian nervous systems, but by the taking into the 

 brain of the hypoglossal, and the appearance of a nerve 

 between it and the vagus, the number of cranial nerves is 

 raised to twelve. The functional kidney of reptiles is the 

 metanephros (p. 445). The mesonephros, though it has 

 quite lost its urinary function, persists in the male as a 

 body called the epididymis attached to the testis, and from 

 it the vas deferens leads. Thus here, as in all vertebrates 

 except the Teleostei, the testis discharges its products 

 through a part of the original kidney, and uses as its 

 vas deferens the original kidney duct (Wolffian duct). 



It is probable that the vas deferens of the Teleostei is only a very long 

 vas efferens. The case of the Mullerian duct, or oviduct in the widest 

 sense, including such structures as shell glands, egg sacks, uteri, etc. , 



