98 MORPHOLOGICAL TYPES 



liver, and the renal veins from the kidneys. Blood returns from 

 the tail by the caudal vein which divides into two ; each portion 

 connects with two veins coming from the hind limb (femoral 

 and sciatic) and runs as the renal portal vein to the kidney of 

 its side. All the blood from the hind regions of the body is 

 not bound to take this course, for instead of engaging in the 

 renal portals it may enter the pelvic veins which run towards 

 one another, join in the midventral line, and proceed forwards 

 as the anterior abdominal. This vein connects with the 

 hepatic portal vein, which collects up the blood from the 

 intestine and takes it to the liver. 



From the lungs, the pulmonary veins return the oxygenated 

 blood to the left auricle of the heart. 



The heart consists of the two auricles and the single 

 ventricle. It is to be noticed, however, that the septum 

 separating the two auricles is perforated, allowing blood to pass 

 from one side to the other. Leading from the ventricle is the 

 conus arteriosus, which, as in Ceratodus, is provided with 

 valves. The truncus represents the ventral aorta very much 

 shortened up ; in its anterior region just before giving off the 

 arterial arches, it is divided into two by a horizontal septum, 

 forming a cavum pulmonale (leading to the pulmonary arch) 

 and a cavum aorticum (leading to the systemic and carotid 

 arches). 



The circulatory system is on the whole very similar to that 

 of Ceratodus. It is to be noted that the separation of the venous 

 blood from the arterial is still far from complete. The blood 

 is oxygenated in the lungs and in the skin. It returns from the 

 lungs to the left auricle by the pulmonary veins, and from the 

 skin to the right auricle by the cutaneous, subclavian, superior 

 vena cava, and sinus venosus. The remainder of the blood 

 entering the right auricle is venous. 



Urino-genital System. — The mesonephric kidneys project 

 downwards from the roof of the ccelomic cavity, covered over 

 by ccelomic epithelium ; they are therefore more easily visible 

 than those of fish. The tubules of the kidneys are drained 

 by the Wolffian ducts which lead into the bladder. In the 

 male, the vasa efferentia from the testis lead through the 



