OCR Text |
Show 346 Ml!. F. E. BEDDARD ON THE [Feb. 16, in front of the first renal artery of the posterior kidney and that the second of these arteries branches into three before entering the substance of the kidney. TROPIDONOTUS FASCIATUS. In this Snake the anterior vertebral artery is exposed for the greater half of the distance which lies between the heart and the posterior end of the head. In the two individuals I have examined it gives off only three intercostals, which occupy about the same position in both. Besides these, the larger-female- (which is perhaps rather better injected) shows a few very minute intercostals with interspaces between the larger trunks. That individual, moreover, possesses a vessel of rather peculiar origin and distribution, which I could not find in the other snake-a male-throughout its whole extent. The artery is a fairly large one and arises from the dorsal side of the vertebral between the last two intercostals, and passing along the wall of the oesophagus enters the parietes anteriorly to the left of the middle and some way in front of the disappearance of the vertebral artery. It may be added that the vertebral artery gives off branches to the oesophagus, as do the carotids, and that some of these spring from the intercostals. Intercostal Arteries and Veins.-There is only a single vertebral artery given off from the right aorta before its junction with the left. Thence forward follows as usual a considerable series of trunks, of which all enter the body-wall accurately in the middle line as fixed by the disposition of the tendons in this region of the body. There are nine of these up to the origin of the superior mesenteric artery : the first lies in front of the liver ; five arise along the course of the liver, and three are posterior to it. The corresponding portal veins do not invariably rise from the parietes in the dorsal median line. The first of the portal series accompanies the second intercostal, but arises from the left side of the dorsal middle line ; it receives a small branch which arises from the parietes nearer to the head, and also much further away from the dorsal median line. The second portal is the stoutest trunk of the series; it arises to the left of the middle line between the third and fourth intercostals. The next portal is a very fine and slender tube arising in front of the fourth intercostal and also to the left side. Then follows a complex parietal portal consisting of three trunks, of which two are in front of and one behind the fifth intercostal. They all lie to the left of the dorsal median line at their point of origin, the third branch more so than the rest. From the latter a slender twig is connected with an equally slender tube arising in this case to the right of the median dorsal line. The next portal trunk is a fairly important one ; it arises in front of the seventh intercostal and to the right side ; it is formed by a slender anterior trunk which arises in a corresponding position further forward. The next two portals are of fair size and arise one a little in front of and the other a little behind |