OCR Text |
Show 1904.] CIRCULATORY SYSTEM IX THE OPHIDIA. 363 of vertebrae is supplied by each intercostal and its superficial continuations; thus I counted from the beginning of the series 7, 7, 5, 3, 6, 3, 3 vertebrae belonging to the area of each intercostal. In one or two cases it is noteworthy that the superficially running portion of an intercostal did not fork either anteriorly or, it m a y be, posteriorly to supply both sides of a vertebra; in such cases one side was supplied by the end of one intercostal and the other side by the anterior end of the next intercostal. Immediately after the liver is a stretch of nine vertebrae served by branches of a continuous superficial vertebral which has two intercostal affluents. The rest of the body is supplied by more numerous intercostals, which generally serve only two successive vertebrae and often only one vertebra. Visceral branches of the Common Aorta.-In the region of the liver a regular series of trunks is given off which supply that organ and the oesophagus. They are closely associated with branches of the portal vein which bring blood from the oesophagus to the liver, so closely that it will be convenient to consider the vessels together. Although the association between the portal vessels and the branches of the aorta is close, there is not an exact correspondence. The first hepatic branch of the aorta is situated about 2 inches behind the anterior end of the liver. It runs straight to the liver, and just before reaching it divides into an anteriorly and posteriorly running branch. The former reaches nearly to the tip of the liver, and takes the place of the two missing hepatic branches of the aorta. About halfway between its origin and its bifurcation a branch is given off to the oesophagus, from which arises immediately a slender twig to the walls of the lung. The portal branch which accompanies it accompanies it closely; its main trunk is derived from the oesophagus, and this lies in contact with the oesophageal branch of the aorta. There is also a branch from the lung-walls also lying close to the lung-branch of the aorta, while the main hepatic stem is accompanied by a portal branch which appears to arise partly from the lung-walls and partly from the walls of the aorta. In front of this first hepatic trunk are two portal vessels arranged at regular intervals, which appear to be serially continuous with the portal branch already described. They are not, however, collecting trunks from the oesophagus, and will be described elsewhere. The next hepatic branch of the aorta arises about an inch further on ; it is accompanied by a portal branch which, like the two last-mentioned, mainly collects blood from the body-walls. This second hepatic artery divides into two much earlier than does the first of this series of vessels. There are altogether 8 of the hepato-cesophageal branches of the aorta which arise at rather irregular intervals and have no relation in position or number to the underlying intercostal arteries. Between the first two hepatic branches there is an unusually wide interval, almost suggesting a missing artery. So far as concerns its oesophageal branch this artery is represented by a long descending |