626 Mil. c. H. o'donoghue on the 



The kidneys eacli possess an anteiior and a median renal artery 

 as before, but instead of one posterior trunk there are at least 

 two, but most often three *. These vessels also send small twigs 

 to their respective vasa defer-entia, and the left anterior renal 

 supplies the fat-body with a large artery. 



The supply to the alimentary canal is also slightly different. 

 The first of the inferior mesenteric arteries arises posterior to the 

 anterior left renal artery, whereas in the female it is anterior to 

 the anterior right renal t. This is followed by a series of about 

 four smaller inferior mesenteric arteries. The various mesenteric 

 arteries are connected by their small branches and so form more 

 or less of a longitudinal system along the gut. 



The origin of the arteries supplying the fat-bodies in both sexes 

 is fairly similar and is somewhat interesting. The anterior part 

 is supplied by branches from the superior mesenteric artery, the 

 next portion by vessels from the right genital artery, and the 

 posterior end is fed by branches from the left genital and left 

 renal supply. In addition to which the posterior branch from the 

 genital artery on each side may in some cases arise independently 

 from the dorsal aorta. All these bi-anches are joined one to 

 the other by small twigs into a longitudinal system running the 

 whole length of the fat-body, but there does not appear to be one 

 unbroken artery, an arteria epiploica, traversing the whole length 

 of the fat-body. 



lY. The Venous System. (PI. LXX.) 



(A) Development. 



The general coux-se of the development of the venous system 

 in Tropidonotus is similar to that of other reptiles [vide Hoch- 

 stetter, 22), but it has some points peculiar to itself [vide Rathke, 

 30, and Hochstetter, 23). 



The first veins to appear are the two omphalo-mesenterics, of 

 wliich the right is somewhat stouter than the left (the reverse is 

 the case in Lacerta), and they open into the sinus venosus. Soon 

 after their appearance the anterior and posterior cardinal veins 

 arise on each side, and their common stem unites with the 

 umbilical vein on each side to form the ductus Cuvieri, which 

 becomes associated with the omphalo-mesenteric veins at the 



* The number of renal arteries varies in different species, being only one in 'Python 

 spilotes and eight in Coronella catenifer, Beddard (1). 



t This differs from the account of T.fasciatus in Heddard (1), where " it springs 

 from the aorta in both sexes close to the second {i. e. left) gonad artery, in front of it 

 ill the male, behind it in the female." Some variation is to be found, however, in the 

 position of this artery in different individuals, for in the females of T. natrix that I 

 liave examined, although it has generally been in front of the right anterior renal and 

 left ovarian arteries, it may be behind these vessels. In the male it is usually behind 

 the left anterior renal arterj-, but it may be in front of it. It has not occurred 

 antorior to the right anterior renal artery' in any male snake that I have examined. 

 Again, we find considerable variation in the number of tliese gut-arteries in various 

 snakes. LacJiesis gramineus has only one, while in the genus Coluber there may be 

 ten or eleven (Beddard, loc. tit.). 



