| OCR Text |
Show 1904.] CIRCULATORY SYSTEM IX THE OPHIDIA. 343 body-wall to one side or the other of the dorsal median line ; but there is no regularity in this arrangement-there is, for instance, no regular alternation from right to left. The first 9 intercostals enter the body-wall to the left of the dorsal middle line ; the tenth to the fourteenth (inclusive) perforate the parietes on the right side; the fifteenth, sixteenth, and seventeenth revert to the left side. The accessory portal veins are nine in number. As a rule, they accompany somewhat closely the intercostal arteries. The first of them thus accompanies the second intercostal, but before entering the liver it is joined by a branch from the body-wall which lies midway between the second and third intercostals. The remaining vessels are close to their respective intercostals, except the 6th vein, which lies between the fifth and sixth arteries, and the ninth, which has a corresponding position further on. As is the case with the intercostal arteries, the intercostal portal veins are irregular in their origin from the right or left of the mid-dorsal line. All those, however, which are accessory portals, opening directly into the liver, arise on the left side, as do the four following intercostal affluents of the portal vein. The fourteenth vessel of the whole series is on the right side. This vessel, moreover, appears to be the last of the parietal portal system. It lies well in front of the origin of the mesenteric-in fact, a little behind the commencement of the narrow pyloric region of the stomach. The anterior vertebral artery becomes lost in the parietes 4 inches beyond the heart and 4 inches from the tip of the snout. It gives off 7 intercostals at not regular intervals ; these are accurately median in position. The artery of the fat-body receives from the aorta only one important affluent which belongs almost entirely to itself. This artery arises from the aorta between the two testes, and, after giving off a very slender twig to the vas deferens of the anterior testes, supplies the fat-body. Anterior branches of the gastric artery supply the fat-body. This Snake has an unusually extensive system of gastric arteries. I counted 15 of them altogether. The first artery supplies one side of the stomach and the second the opposite side. The remaining arteries show with some irregularity the same alternation. The tenth gastric artery sends off two slender twigs backwTards for the supply of the pancreas and adjacent viscera. It also gives off a backwardly running branch which joins the gastric branch of the superior mesenteric and also divides into two trunks, one for each side of the stomach. The next artery for the supply of the viscera which arises after the gastric is the superior mesenteric. This artery has the usual two branches ; but before it divides into these it gives off a slender forwardly running branch to the pancreas and spleen. This branch runs to the left of the portal vein, while the gastric branch runs to the right of the same vein. The spermatic and renal arteries have no definite relations to |
