1906.] ANATOMY OF THE OPHIDIA. 19 



in the foetal snake, the right-hand vein is depicted as joining the 

 vena cava, while the left-hand vein is lost in the liver plexus. 

 The umbilical vein was turgid with blood and of equal calibre 

 with the efferent renals or other principal blood-vessels of the 

 reptile. It is noteworthy that the umbilical vein until it 

 reaches the region of the liver appears to run in an accurately 

 median course. This clearly suggests that only one umbilical 

 vein is present. In any case only this vein is obvious, unless the 

 vein identified by me above with the ophalomeseraic be really the 

 left umbilical. 



In any case it is clear that this vein belongs to the foetal circu- 

 lation, inasmuch as it passes through the navel to the foetal 

 membranes, and that it has nothing to do with what ai-e usually 

 held to be the equivalents in the Ophidia of the anterior abdominal 

 vein or veins in other reptiles. A remarkable fact about this 

 vein is not merely its presence in the young when born and able 

 to feed for themselves, but its persistence in the fully adult 

 snake. In an Anaconda * {Uunectes imtrinus S ) dissected in 

 May 1904, which was acquired by the Society in 1899 as an 

 adult, I found a vein ending on the fat-body posteriorly which ran 

 over the liver (i. e. ventrally of it), but did not draw blood from 

 that organ anywhere, and emptied itself into the vena cava 

 anteriorly shoi-tly aftei- that vein had freed itself from the liver. 

 It is plain that this vein is that which I call umbilical in the 

 young Anacondas. I have no i-ecord of such a vein in Python, 

 nor is one figured by Jacquart f nor by Gadow + in Boa. 



It seems quite certain that this vein is the homologue of that 

 vein in Birds which passes between the lobes of the liver, recurring 

 in the falciform ligament. Hochstetter has proved § that the 

 vein in question, variously termed " anterior abdominal," " epi- 

 gastric," and " umbilical," is the persistent umbilical vein of the 

 embryo. It follows therefoi-e that it cannot be the homologue of 

 the anterior abdominal vein of the Lacertilia, which has been shown 

 to be a new structure, having nothing to do with the foetal umbilical 

 vein. There are therefore among Sauropsida two morphologically 

 distinct veins or systems of veins which convey blood along the 

 ventral surface from the posterior region of the abdomen to the 

 liver or to the hepatic vein, and which are undoubtedly super- 

 ficially similar, so much so that embryology alone has been able 

 to decide the question of their distinctness. 



The coincidence of these two veins in Eunectes solves the problem 

 so far as concerns that species. At present so little is known of 

 the venous system in the Ophidia, so few types have been 

 examined from this point of view, that so far the Anaconda is 

 the only snake in which the two forms of abdominal vein have 

 been met with together. It is impossible therefore to build up 



* Since this paper was written I have found the vein in a second adult male 

 jE. murinus. 



t Ann. Sci. Nat. (4) iv. 1855. 



X Bronn's Thierreich, Bd. vi. Rept. Abth. iii. Schlangen. 



§ Morph. Jahrb. xiii. 1888, p. 575. 



2* 



