120 ON THE ANATOMY OF CERTAIN SNAKES. [May 17, 



E. coniciis, the character may, I take it, be regarded as a genuine, 

 if small, difference. 



Secondly, the right lobe of the lung extends further back in 

 Eryx jaculus and JE. johni. In those species it reaches the gall- 

 bladder ; in Eryx conicus it falls short of the gall-bladder by at 

 least an inch. 



The superior mesenteric artery arises in Eryx jacuhts and 

 E. johni distinctly in front of the gall-bladder. In Eryx conicus 

 its point of origin is as distinctly behind the gall-bladder. This 

 character is perhaps less likely than some others to prove of value 

 as an absolute mark of distinction. 



More important are other differences in the vascular system. 

 In Eryx jaculus, though it is the smaller species, there are appa- 

 rently, as a rule, two arteries supplying each kidney ; in Eryx 

 conicus there is but one to each kidney : and here apparently 

 E. johni agrees with E. conicios. The intercostal arteries have a 

 different arrangement in the two species. In E. jaculus there is a 

 well-developed posterior vertebral artery formed by the junction of 

 irregularly arising intercostals ; in E. conicit,s this does not exist 

 (except as the merest rudiment). The paired intercostals com- 

 mence further forward in E. jacuhos than in E. conicus. E. johni 

 in these particulars is somewhat intermediate. In E. jaculus 

 there is a double connection of the anterior abdominal vein with 

 the afferent renals posteriorly ; in E. conicus this occurs only 

 on one side. E. johni agrees with E. jaculus. In relation to 

 these anatomical differences, which appear to me to be fully as 

 great as those which distinguish either species from Eunectes, I 

 would draw attention to the restricted range of E. conicus and to 

 the wider distribution of E. jaculus and E. johni. 



Resuine of principal facts. 



It may be convenient to deduce from the foregoing pages the 

 main facts in the vascular system of the Boid^e examined ; such 

 may be divided into two heads, i. e., those which appear to argue 

 a basal position among the Ophidia, and those which are of sys- 

 tematic importance in the group. As to the former it may be 

 noted that 



(1) The heart is always without the least trace of a guber- 



naculum cordis. 



(2) The two aortae are usually equisized at their point of union 



to form the dorsal aorta. 



(3) The renal and gastric arteries ai'e much fewer in number 



than in other Ophidia, the former consisting generally of 

 only one artery to each kidney. This distribution has no 

 relation to the size of the kidney. 



(4) Tlie intercostal arteries are always symmetrical and for 



the most part regular in their ai-rangement, frequently in 

 regular pairs. 



