VEINS OF REPTILES. 505 



cavity, receiving the segmental or vertebral veins, and terminates 

 in the left precaval vein. The jugular and the axillary trunks 

 unite to form a precaval vein, fig. 332, v*, on each side, the left of 

 which as usual passes behind the auricles to the postcaval orifice 

 of the sinus. 



In the Chelonia the blood from the tail and hind limbs is 

 conveyed along the plastron by a pair of ' umbilical ' or sub- 

 abdominal trunks, which receive the veins of the large allantoic 

 bladders, and the meseraic veins, to form the great portal trunk. 

 A small derivative branch from the posterior part of each umbi- 

 lical communicates with lumbo -dorsal vertebral veins, and with 

 some veins from the genital organs to form the reni-portal veins. 

 The renal veins unite with the ovarian or testicular veins to form 

 the postcaval, which traverses the liver and receives there the 

 hepatic veins : the wide and short trunk, fig. 336, v, then termi- 

 nates in the auricular sinus. The blood is returned from the 

 head and fore-limbs by the jugulars, figs. 302 and 304, i, i, and 

 from the axillary veins, ib. h, h. Each axillary unites with the 

 jugular of its own side to form a precaval vein : the right and left 

 precavals enter separately the auricular sinus, the left precaval 

 opening near the postcaval vein. 



In the Crocodile, the caudal vein, on entering the abdomen, 

 divides into two trunks : each unites with the ischial and iliac 

 veins of its own side and advances towards the kidney. Here 

 the trunk sends off a reni-portal vein, and is then continued 

 towards the hepato-portal system. The renal veins from the inner 

 side of the kidneys unite to form the postcaval, fig. 339, Y, 

 which receives the left precaval, fig. 340, v**, at its entry into the 

 auricular sinus, ib. S : the hepatic veins open separately into the 

 contiguous end of the sinus, fis;. 339, S. The blood from the head 



O O / 



and forelimbs is conveyed to the heart, as in other Reptiles, by a 

 pair of precavals, of which the right, ib. v, terminates in the fore- 

 part of the sinus, and the left traverses the back part of the heart, 

 receiving the coronary veins, to join the postcaval or to terminate 

 near its auricular orifice. 



89. Heart of Reptiles. In Lepidosiren the vein from the lung- 

 like air-bladders traverses the auricle and opens directly into the 

 ventricle. In Siren the pulmonary vein dilates, before commu- 

 nicating with the ventricle, into a small auricle, which is not 

 outwardly distinct from the much larger auricle receiving the 

 veins of the body. 1 This is remarkable for its large size, thin 

 walls, and hollow, fimbriated processes, which overlap and almost 



1 XXXIII. 



