1906. J ANATOMY OF THE OPHIDIA. 37 



nasicornis. Each of these two is closely accompanied by an artery. 

 The larger enters the heart in common with the azygos, and runs 

 forward on the right side of the body as far as the head. It is 

 much more slender in its most anterior region than near the heart. 

 This vein gives off to the right a sei-ies (I counted seven in the 

 most fully developed specimen) of branches to the parietes, which 

 immediately plunge into the thickness of the body- wall after a 

 very short free course. From the left arise a smaller number of 

 veins which have a longer course. Of these I found not more 

 than three. They arise at right angles from the main trunk, and 

 cross the body to the left side of the dorsal median line. Here 

 they appear to become continuous with a longitudinal trunk which 

 runs a considerable way towards the head and posteriorly as far 

 as a little way down the liver. This vein runs much further from 

 the dorsal middle line than the right jugular and the right azygos. 

 The branches, soon after leaving the jugular, send off a twig to the 

 oesophagus. 



The longitudinal vein of the left side of the body, supplied by 

 branches from the right jugular, represents, as I imagine, the left 

 anterior cardinal, the right vein being the persistent right anterior 

 cardinal. Their mutual asymmetry with reference to the median 

 lines of the body is remarkable. It is possibly to be accounted for 

 by the pressure exerted by the trachea and lung pushing the vein 

 further away from the middle line. The right azygos vein appears 

 at first sight to be of less extent than a more careful examination 

 shows it to be. In three of the specimens which I examined this 

 vein, which is of considerable calibre, appeared to end at about the 

 level of the ventricular apex; but in a fourth example it was 

 distinctly continued back by a very slender prolongation to a 

 point quite on a level with the middle of the liver. It is note- 

 worthy that the azygos not only gives off' branches to the intercostal 

 spaces along which it runs, but that close to its origin — or rather 

 debouchement into the auricle — it sends out a forwardly-running 

 branch, which ought, so to speak, have been furnished by the 

 anterior cardinal of that side of the body. 



In addition to the right jugular, which is a vessel as thick as 

 any in the body, and the rudimentary left jugular, which is prac- 

 tically a branch of it, though morphologically, as I imagine, a 

 distinct vein, an internal jugular runs along the trachea. This 

 vein, like the right jugular or anterior cardinal, is closely 

 accompanied by an artery. The artery, however, like the vein, is 

 thinner than are the pair which run along the body- wall on the 

 right side. Whether there is a corresponding and less developed 

 vein for the opposite side of the trachea, I am unable to say. 



In the arrangement of these anterior veins Bitis stands at the 

 opposite pole from the Anaconda, whose anterior veins have been 

 considered above. In the latter serpent all four veins, viz. both 

 anterior cardinals and two internal jugulars, exist. In the Yiper 

 the reduction is striking. Intermediate conditions are offered by 

 Boa^ in which, according to Gadow's figures, the veins of the neck 



