1904.] AXATOIHy OF CERTAIN SHAKES. 113 



tnuriniis, Eryx johni, and Eryx conicus each kidney had only one 

 renal artery. In Eryx jacidus there was some variation in the 

 two examples studied. In one there were two renal arteries for 

 each kidney ; in the other the left kidney had two arteries, the 

 right only one. Here, it may be remarked in passing, is an apparent 

 difference between the two species of Eryx investigated by me, 

 which I shall refer to again later. 



Now, as the kidneys of Eryx are very short * and those of 

 Coluber catenifer long, as they are in the majority of snakes, it 

 might be held that the arterial blood-supply had merely a relation 

 to length. That the character is one peculiar to the Boidse seems 

 to be shown by the case of Eunectes murinus, for in this serpent 

 there is only one renal artery to each kidney ; and yet those 

 organs, in the individual which I dissected, measured respectively 

 15| and 12| inches in length. 



§ Veins of the Posterior Abdominal Region in Eunectes. 



The caudal vein emerges from the thickness of the parietes some 

 way behind the cloaca. When it reaches the level of the cloaca, 

 two veins, asymmetrically placed with regard to one another, 

 join it. I suppose that these are the equivalents of the 

 ischiadic veins of Lizards. Further forward, between the cloaca 

 and the very anteriorly situated kidneys t, the caudal vein divides 

 at once into three branches. The middle one of these is the 

 right and larger anterior abdominal vein. To the left of this 

 arises the afferent renal vein of the left kidney, and to the right 

 of the anterior abdominal a vein which runs over the viscera to 

 the dorsal surface of the body, where it enters the parietes to the 

 left of the middle line, after running both forwards and backwards 

 for a short distance. I am inclined to regard this vein as the equiva- 

 lent of the lateral abdominal vein of its side in the Lacertilia. Its 

 place of origin agrees with such an homology, and the shortness 

 of its course within the body- wall is no reason against the com- 

 parison, since it is of varying length among the Lacertilia. It 

 might be held that this vein is in reality only the proximal end 

 of the left afferent renal which has lost its connection with the 

 remainder of that vein, were it not for the conditions observable 

 in Eryx to which I recur later (see p. 114). There is, in fact, no 

 afferent renal on this side of the body springing from the caudal 

 vein and cori-esponding in origin to the fully developed afferent 

 renal, whose origin on the other side of the anterior abdominal 

 has been already referred to. It rises, I presume, from the caudal 

 vein further back. 



* In Tlryx johni, which measured 26 inches from snout to vent, the kidneys were 

 respectively f inch (right kidney) and 1 inch (left kidney) in length. In JE.jacuhis 

 of lof inch length to vent, the kidneys were proportionately larger, i. e. | inch and 

 1 inch, and in E. conieus of 27 inches this was also the case ; they measured 1^ 

 and 1^ inch. 



t The kidneys are well known to occupy a very anterior position in the Boidse. 

 It has not, I think, been noted that Eri/x as well as JEhmectes agrees in this with 

 Python and Boa. 



Paoc. ZooL. Soc— 1904, Vol. II. No. VIII. 8 



