536 



URODELA 



[CH. 



openings 



of the two superior venae cavae. The inferior cava 

 coalesces with the hepatic veins 

 returning blood from the liver : 

 these thus lose their independent 

 openings into the sinus venosus 

 which they had in the Dog-fish. 

 In its hindermost portion between 

 the kidneys the vena cava pins 

 the subcardinal veins, i.e. the 

 collecting trunks formed by the 

 blood which has percolated 

 through the kidneys from the 

 renal portal, and which open into 

 the posterior cardinal veins in 

 front. 



So far the peculiarities of the 

 newt are shared by the Dipnoi : 

 but there remain two veins highly 

 characteristic of Amphibia. The 

 musculocutaneous vein re- 

 ceives blood from the skin and 

 pours it into the subclavian ; we 

 have already seen that the skin 

 is a very important breathing 

 organ, and this vein returns the 

 blood which has been oxygenated 

 in the skin to the heart. The an- 

 terior abdominal vein arises on 

 the ventral side of the body near 

 the cloaca from the union of two 

 forks given off by the femoral 

 veins ; it runs forward in the mid- ventral line, eventually joining 

 branches of the portal vein and entering the liver. This vein is 

 found also in the lower Reptiles and in the embryos of Mammalia, 

 where it is of the utmost importance in both nutrition and respira- 

 tion ; it has been compared to the lateral veins of Chondrichthyes 

 (see p. 463) which are supposed to have become shifted inwards 

 towards the mid- ventral line and to have partly coalesced. 



When the veins are cut away it is possible to follow out the 

 arteries. There is no ventral aorta, since on each side three arterial 

 arches arise in a bunch from the front end of the tubular conus. 



10 



FIG. 261. Diagram to show arrange- 

 ment of the principal veins of an 

 Urodele. 



1. Sinus venosus, gradually disappear- 

 ing in the higher forms. 2. Ductus 

 Cuvieri = superior vena cava. 3. In- 

 ternal jugular = anterior cardinal 

 sinus. 4. External jugular = 



sub-branchial. 5. Subolavian. 



6. Posterior cardinal, front part. 



7. Inferior vena cava. 8. Renal 

 portal = hinder part of posterior car- 

 dinal. 9. Caudal. 10. Sciatic. 

 11. Femoral. 12. Anterior ab- 

 dominal. 





