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Show 360 Mil. E. E. BEDDARD OX THE [ I'Vb. 16, corresponding exactly to the number of vertebrae, and show but the faintest traces of commencing disappearance. That is to say, the arteries are of fair size and equisized ; in only one case did I observe an artery reduced to thread-like dimensions. Furthermore, the arteries are accurately median at the points where they enter the parietes, and the foramina through which they enter are larger than the arteries themselves. Intercostal Arteries.-These arteries commence to arise from the right aortic arch before its union with the left. But in this region they do not form a continuous series; there were only three. After the junction of the two aorta? the intercostal arteries still retain the median point of entrance into the parietes, a position which distinguishes them at once from the intercostal veins-as also in Lachesis gramineus. The arteries are very numerous, and there are occasional stretches of ten or a dozen which are continuously at regular intervals. In a very few cases the arteries are so excessively slender as to suggest commencing disappearance. I counted altogether 94 of these arteries, to which I think 3 or possibly 4 are to be added. The total is only just under the 100. As may be inferred from their median position, none of these arteries are paired ; nor can an anterior-series be distinguished from a posterior, save that the first few are rather farther apart than they become later. Intercostal Portal Veins.-These veins are, as is usual, few in number when compared with the intercostal arteries. I counted altogether 13 of them, of which the anterior 6 are less important than those which follow. The first 6 lie opposite to the liver, and are therefore not direct affluents of the main trunk of the portal vein. The first arises after the 7th intercostal artery * ; the next 5 are separated by fewer intercostal arterial trunks. These first 6 veins spring from the body-wall to the left of the median dorsal line. The 5 following intercostal portals spring from the right side of the dorsal middle line. The first of this series, i. e. the 7th of the entire series, is a little beyond the end of the liver. The next two, close together, accompany the posterior gastric artery ; the 10th in a similar way accompanies the superior mesenteric, while the 11th and 12th correspond respectively to the testicular arteries. The latter vein and the 13th, which is in the kidney-region, emerge from the body-wall on the left side of the dorsal median line. It will be noticed that some of these veins spring from the middle line of the parietes. The spermatic artery which supplies the anterior testis is a single vessel which enters the gonad near to its posterior end. It there becomes longitudinal and runs forwards as well as backwards along the vas deferens. It is the first artery for the supply of the viscera which is given off by the aorta after the superior mesenteric. This longitudinal testicular trunk gives off one branch anteriorly and two branches posteriorly to its origin from the * Counting from the junction of the right and left aorta.-. |
