OCR Text |
Show 470 MR. F. E. BEDDARD ON THE [Nov. 28, after giving oft' at any rate one intercostal twig, divides into two slender trunks diverging right and left. Each of these separates from itself immediately after its own origin a vessel which rapidly plunges into the thickness of the body-wall in the middle line, and which represents on either side the anterior vertebral arteries of other Lizards. In spite of the limbless character of this Ophisaurus, the subclavians are still more distinctly recognisable as such than they are in Amphisbcena. The left aorta gives off several vessels to the oesophagus before joining the right aorta, but no intercostals. On the other hand, the right aorta gives off several intercostals before joining the left. Ratlike mentions oesophageal arteries as arising from the right aorta. The carotid artery does not pass up the neck alongside of the trachea. But the windpipe is, as in other Lacertilia, accompanied by an artery. This ai'tery, however, in Ophisaurus is only to be seen on the right side of the trachea; on the left there is at most a rudiment of the same. It gives off branches to the thyroid which correspond to those given off on the left side by the carotid arch before it gives off the carotid artery. This tracheal artery arises, as do the corresponding pair in Hatteria, &c., from the pulmonary artery. In Ophisaurus it is accompanied by a vein of larger calibre than itself, which runs up the neck in close contact with it and again only on the right side. On the left I could discover no traces of a corresponding vein. This vein joins the anterior cava. The asymmetry in this part of the arterial system is noteworthy, for the reason that it is the only part of the arterial system which shows, in correspondence with the snake-like habit of body, any traces of an asymmetry. The dorsal aorta gives off ventrally a regular paired series of intercostals, which fail apparently nowhere and are even and regularly paired throughout. (Esophageal and Gastric Arteries.-A striking feature of this Lizard as compared with many is the very large number of trunks arising from the aorta which supply the oesophagus and stomach. There are two or three cesophageal vessels arising from the left aorta before it joins the right. After the junction there are seven small arteries still supplying the oesophagus. Of these, which are not mentioned by Rathke, the first four arise from the aorta itself. After these come three trunks, which arise not from the actual aortic trunk but from the intercostal vessel of the left side. All of the oesophageal arteries are very small and at the same time very convoluted in their course. Following them are five gastric trunks, which are all of greater calibre than the oesophageal vessels. The last three of these are particularly important. A considerable gap separates these gastric vessels from the three chief arteries which end upon the walls of the intestinal canal. Hochstetter has figured three variations in point of origin of these threearteries. In the individual dissected by myself I found one of these three arrangements to |