| OCR Text |
Show 1904.] CIRCULATORY SYSTEM IX THE OPHIDIA. 335 2nd branch is posterior, and passes back along the intestine to join the first of the rectal vessels. It is perhaps noteworthy that the point of origin from the aorta of the two mesenteric; vessels differs ; the superior trunk arises laterally from the aorta, whereas the inferior mesenteric arises from that trunk in the mid-ventral line. This conceivably suggests a previous state of affairs (phylogenetically speaking) when the intestine coiled ventrally in its middle and posterior regions. Text-fig. 67. Part of arterial system of Zamenis mucosus. F.B., fat-body arteries; Infmer.. inferior mesenteric ; Int., intercostal arteries ; Bee, rectal arteries ; Ben., renal; Sr.V., suprarenal portal veins ; T., testis ; Vci., vena cava. Tlie first of the rectal vessels, however, originates laterally like the superior mesenteric. It springs from the aorta in a position almost exactly between the two testes and about | inch in' front of the inferior mesenteric. It has also, as will be mentioned, an intimate relation to one of the arteries of the fat-body (see p. 337). The trunk runs backwards, crossing the inferior mesenteric dorsally, and reaches the intestine at a point about opposite to the end of the first third of the posterior testis. Its behaviour when it reaches the gut is precisely that of the mesenteric arteries; it divides into two branches, an anterior and a posterior, so that it aids in the formation of a continuous sub-intestinal vessel running from end to end of the gut. The second Rectal Artery arises behind the posterior testis. and also springs laterally from the aortic trunk. Moreover, it has exactly the same relations to a fat-body artery arising at this spot as has the anterior rectal. The third Rectal Artery arises laterally (and on the same side as the two anterior arteries) from the aorta just behind the origin of the second of the renal arteries supplying the left kidney. Behind this there are, at any rate, four more arteries arising at much shorter intervals. There may be more, but the injection was deficient in this region of the body and rendered observation difficult. It is noteworthy that the rectal arteries become more crowded towards the end of the body ; the 1st and 2nd are further apart than the 2nd is from the 3rd. |
