20 MR. F E. BEDDARD ON THE [Jan. 16, 



much in the way of an attempted explanation without further 

 facts. In the meantime the facts suggest that Eunectes offers a 

 transitional state of affairs between the retention of the umbilical 

 vein as the vein of the abdomen and its replacement by the sub- 

 sequently developed anterior abdominal. It is exactly analogous 

 to the relations between the posterior cardinals and the vena cava. 

 In the primitive Ceratodtis we have one cardinal persisting in its 

 entirety and at the same time an undoubted vena cava posterior*. 

 In higher types the posterior cardinals are more or less rudi- 

 mentaiy, and the vena cava alone is concerned with the circulation 

 of the region of the body formerly served by the cardinals. 



Replacements of this kind are familiar to morphologists in 

 connection with many organs. 



It is not without significance, in my opinion, that this state of 

 affairs has been discovered in a snake, and especially in an un- 

 doubtedly primitive snake. That the Squamata form one group is 

 probably the opinion of every zoologist at present. It is further 

 clear that no existing group of Lizards is much nearer to the 

 snakes than any other. The origin of the Oph'idia must have 

 been from some earlier type. This may land us some way back 

 in the history of a group which with Hatteria appears to me to 

 represent the archaic reptilian structure more than any existing 

 group of Reptiles. It is possible that in the extensive fat-body 

 of snakes we have the cause of the oiigin of the double anterior 

 abdominal veins. The only fragment of evidence, however, which 

 points to a large fat-body as a character of the ancestral Squamata 

 is its large size in ^m^?A?"s6^?i« t. But this evidence is not to be 

 neglected. The growth of the abdominal veins would render the 

 umbilical superfluous, they taking on its function of drawing blood 

 from the body- walls. 



Systeim of Anterior Veoice Cavce. — The veins of the anterioi- 

 region of the body consist of four main trunks, which of course 

 unite in pairs to form the two superior cavpe. The left tracheal 

 unites with the left anterior vertebral and each right-hand vessel. 

 It is notewoi-thy that the two anterior vertebral veins run super- 

 ficially at equal distances from the median anterior vertebral 

 artery. Each vessel lies in a furrow between longitudinal bands of 

 musculature. The vertebral vein receives a large branch from the 

 parietes just before joining the tracheal vein ; the conjoined vein 

 then receives just before its entrance into the heart the azygos, 

 which is only present upon this side of the body. The azygos is 

 short, and only collects blood from fovir intercostal spaces. Of 

 the four branches which constitute it, one is especially large, and 

 comes off exactly opposite to the point of entrance of the azygos 

 into the Ductus Cuvieri. In the second specimen the azygos 

 was much the same. 



Epigastric Vein. — This vein has already been referred to in 



* See W.B.Spencer, in "The ^lacleay Memorial Volume" published bj' the 

 Linnean Society of New South Wales, 1893. 

 f V. Bedriaga, Arch. f. Naturgeschichte, Jahrg. 50, 1885, pi. iv. fig. 2, Fk. 



