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Show 112 MR. F. E. BEDDARD ON THE [May 17, In Eryxjohni the same series of oesophageal branches arising from intercostals are present. They arise from intercostals partly belonging to the right aortic arch, and partly to those arising from the common trunk. The third intercostal, after the union of the two aortse, gives off a slender vessel which runs forward and joins a vessel arising from the last but four of the intercostals belonging to the right aorta. This longitudinal trunk gives off several lateral vessels. The third, fourth, and fifth of the intercostals of the right aortic arch also give off single oesophageal vessels. I have pointed out in another paper* that the Lizard Pygopus is unusual by reason of the fact that some of the visceral arteries arise from intercostals instead of directly and independently from the aorta. In Eryx johni precisely the same mode of origin occurs not only for oesophageal arteries, but for a fat-body artery. This springs from the right-hand intercostal of the seventh pair after the posterior renal artery. I observed the exact converse of this state of affairs in Tropidonotus fcisciatus. The right aorta gives off intercostal branches, but no twigs to the oesophagus that I could find. On the other hand, a single parietal vessel, accompanied closely by a vein, enters the parietes a good way to the left of the middle dorsal line and arises unmistakably from the left aortic arch, which also, of course, gives off several branches to the oesophagus. Gastric arteries.-The fact that in Eryx there are only two f and in Python spilotes only three gastric arteries, appears to me to be an archaic point of structure in these Boid snakes. Among the Ophidia generally there is frequently a large number of gastric arteries. For example, in the genus Coluber I have found as many as ten or eleven. The reduplication of these and other arteries, so characteristically Ophidian, seems therefore obviously to mark the more specialised members of the group. The absence of, or less, reduplication is not therefore inconsistent with the less modified, more archaic, structure. Ovarian arteries.-It is at least rare among snakes i for the arteries supplying the gonads to arise from the aorta opposite to each other. As a rule one spermatic or ovarian artery follows the other in relation to the asymmetrically placed gonads. Nevertheless in a female Eryx conicus the two arteries arose side by side. _ They immediately follow, as is usual, the superior mesenteric. The paired condition of these arteries seems to me to be a primitive feature in the organisation of this snake. Renal arteries.-It is the general rule among the Ophidia for each kidney to be supplied with a considerable number of arteries. There are, for example, as many as eight in Coluber catenifer. Among such Boidse as I have examined, the number is invariably one or two arteries only to each kidney. In Python sebce, Eunectes * Above, p. 12. f I could find only one in Eryx johni. I I have not myself observed a single instance in the Ophidia except in the case mentioned above. |