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Show 1904.] CIRCULATORY SYSTEM IX TU E OPHIDTA. 353 aorta and vertebral artery, but a special lymph-tube ensheathes the outgoing intercostal artery, and beside it another lymph-tube (see text-fig. 70, p. 352) which does not contain an artery, but whose presence possibly indicates the former existence of such an artery. Traced anteriorly, the vertebral artery gives off a branch to every intervertebral space. Some of these, however, are excessively fine and might readily be missed. There are fourteen, however, which are stout arteries and could not be missed, which lie between the origin of the anterior vertebral and the point at which it disappears into the thickness of the parietes. It is interesting to note that none of the intercostal branches seem to be really missing; they are simply unequally developed. All these arteries are exactly median in their point of entrance into the parietes, and a clean-cut circular orifice in the parietes considerably larger than the artery permits its passage. The right aortic arch gives off two intercostals before it joins the larger left aortic arch. As is the rule in the Ophidia, the intercostals in the anterior region of the " thorax " are much less numerous than they are posteriorly. But here there are not indications, as there are in the cervical region, of missing intercostals. This suggests the length of the trunk is an older feature of the Ophidia than the length of the neck. This snake differs from some others in the fact that the bulk of the intercostal arteries beginning quite anteriorly divide near to the dorsal middle line, so that the entrance into the parietes is on both sides of the vertebra. The very first of the intercostals, and after two others which are single and enter on the left side, is another which bifurcates ; thereafter follows a series which regularly bifurcates. Further back the usual and irregular alternation of the arteries is to be noted. As this more or less regular bifurcation of the anterior intercostal arteries occurs in both specimens, it m a y fairly be regarded as typical of the species. Gastric Arteries.-The gastric arterial system in this snake shows certain broad differences from that of Coluber melanoleucus. It is possible in the first place to distinguish two series of gastric arteries, small and large. This is not simply a question of larger posterior and smaller anterior gastric arteries, such as occur in Coluber. In Coronella getulct there are a few large arteries which vary somewhat in size among themselves, and a host of minute arteries of almost microscopic size. There is no series of transitions between the minute and the large arteries; the latter lie among the former. The minute arteries form a complex network in the mesentery of the stomach, though with very large meshes, and end upon the surface of the stomach. This network appears to join the trunks of the larger gastric arches. Of the large gastric arteries there are five, of which the first and the last are not purely gastric but also supply other organs. The first gastric artery arises just at the junction of the oesophagus and stomach, and just at the end of the liver. It is much larger than the preceding hepatic arteries, so that there is PROC. ZOOL. Soc -1904, VOL. I. No. XXIII. 23 |
