ABNORMAL VEINS IN THE FROG. 32? 



to showing an abnormal origin of the mesenteric vein from 

 the capillaries of the lung, the specimen exhibited abnormal 

 htemorrhoidal and splenic veins, which apparently ended in the 

 pulmonary capillaries. The blood conveyed by these two latter 

 vessels could therefore be returned from the lung either by the 

 left pulmonary vein or by the abnormal origin of the mesenteric 

 vein. A diagram of the arrangement found will make the 

 description clear. In the specimen from which the drawing 

 was taken, the lung had been inflated, 



• Quite recently, Dr Ernest Warren ^ has described three in- 

 stances in which in frogs he has met with a vessel passing from 

 the lung to the hepatic portal system. In one case he found 

 that an artery arose from the posterior mesenteric and passed 

 to the apex of the lung, and the corresponding vein bifurcated, 

 one branch being continued into the renal portal, and the other 

 into the hepatic portal via the ha^morrhoidal vein. Dr Warren 

 points out that the condition he described is somewhat similar 

 to that found in a teleosteau fish, in which the mesenteric artery 

 gives a branch to the air-bladder, from which the blood returns 

 into the portal system. He suggests that the condition is 

 explained as one of reversion. 



4. An Innominate Vein. — As is well known, the usual plan 

 of the pre-caval system of veins in the frog is that of a right 

 and left pre-cava, opening separately into the sinus venosus, and 

 draining the right and left sides respectively without apparently 

 any definite anastomosis across the middle line. Each pre-cava 

 is made up by the confluence of three veins — external jugular, 

 subscapulo-jugular (usually, though erroneously, named innomi- 

 nate), and subclavian. In the abnormal specimen now under 

 consideration, the arrangement on the left side was as usual, but 

 on the right side the pre-cava was occluded. It could, on that 

 side, be traced as a tiny vessel for a very short distance beyond 

 the junction of the external jugular, subscapulo-jugular, and sub- 

 clavian, and was then lost, never coming into relation with the 

 sinus venosus at all. Passing across the middle line in front 

 of the anterior border of the heart, and ventral to the great 

 arteries, however, was a large vein connecting the point of con- 



^ Anatom. Anzeig., xviii. pp. 122-3, 1900. 



