OCR Text |
Show 624 MR. F. E. BEDDARD ON THE [May 29, these unite some little way before they reach the liver. Shortly after reaching the liver, but before burying itself in the substance of the same, the vein receives another which is made up of three tributaries, of which two are from intercostal spaces immediately following those which give rise to the first two of these dorsal parieto-hepatic branches. The third vessel arises from the parietes laterally. The vein formed by the union of the five venous twigs which have been just enumerated enters the substance of the liver considerably to the right of the entrance of the right anterior abdominal vein. Between the two enters a vein which conducts only blood from the lateral parietes. As is also shown in the figure referred to, the posterior vertebral artery arises from the aorta and reaches the parietes between the two anterior intercostal veins. This is the same on both sides of the body. These branches from the azygos to the liver are also arranged with perfect symmetry in relation to each series on the two sides of the body. They commence in each case opposite to the same vertebra. The actual sizes, however, of the several branches differ, though the total volume appears to me to be much the same. On the left side there are two thick trunks which are not far short of the azygos itself in calibre. These join before reaching the edge of the left lobe of the liver. After joining, the common trunk bifurcates into a wider and a narrower branch. The wider branch enters the liver at the apex of the left lobe immediately. The narrower branch receives almost at once a thinnish parietal branch, and passes downwards along the free posterior edge of the left liver-lobe to some way along that margin, though considerably short of the middle line. Here it enters the liver-substance independently of not oidy the anterior abdominal vein, but also of the lateral parietal and considerably to the left of both these veins. The wide calibre of these various veins contrasts with the very narrow corresponding intercostal arteries and their branches. This contrast is much more marked than in other regions of the vascular system, where the arteries and veins are more equisized.~ I have examined only one individual of Crocodilus cataphractus, and it might therefore be supposed that the conditions observed being subject to variation were hardly distinctive of the species. Whether this be so or not I do not, know; but in any case there is so considerable an agreement between two individuals of Osteolcemus tetraspis of which I have dissected the veins under consideration, that I describe the following conditions with some confidence as distinctive of that species. On the left side of the body there are four vessels belonging to the system of veins which is at present dealt with. The three anterior of these belong,* entirely and only to the vena vertebralis posterior, and they arise from it. The actual way in which these vessels join and rejoin with each other before reaching the liver is illustrated in the subjoined figure (text-fig. 105, p. 621), and is rather more complicated than the arrangement found in Crocodilus cataphractus and C. acutus; that is to say, there are anastomoses between the trunks |