OCR Text |
Show 1903.] ANATOMY OF TnE JAPANESE SALAMANDER. 301 however, the oviducal mesentery leaves the common dorsal mesentery, and goes to the right and to the left to follow the oviduct to its internal aperture. The aorta itself is removed by quite a long distance from the dorsal median line, from which the dorsal mesentery, over an inch wide in parts, suspends it. It should be observed that this membrane is continuous and not fenestrated as it is in the frog, where the aorta also does not lie close to the backbone. Within this mesentery are suspended the intercostal arteries and certain portal veins, both of which are described elsewhere (see p. 312). The halves of this mesentery are so loosely attached to each other that the slightest pull brings them apart. I a m disposed to think that this ready separation argues a lymph-space or spaces of considerable extent within the cavity of this dorsal mesentery. The above description of the mesenteries has been given partly to serve for a comparison with Menopoma. The differences between the two forms are not, however, great. In the first place, the left lung is very much shorter than the right in Menopoma. In Megalobatrachus it is slightly longer. Nevertheless, in Menopoma the free tip of the lung to which no mesentery is attached is proportionately much longer than in Megalobatrachus. Finally, the left lung of Menopoma is connected only with the oesophagus. This membrane, however, runs for a little distance over the mesentery attaching the stomach to the aorta, and is a trace of the former greater extension of the lung. The gastro-hepatic ligament bears, of course, the gastric and oesophageal branches of the portal, which show differences in the two animals. In both, the oesophageal portal is quite distinct from the gastric, and enters the liver at about the middle of its length. In Menopoma this trunk is formed by the union of two equally sized vessels. In Megalobatrachus there is but one. In the larger specimen of this genus, moreover, the condition was still more specialised ; there was no separate oesophageal trunk at all. Furthermore, in Menopoma the gastric trunk consisted of two main trunks meeting near to their entrance into the liver posteriorly; the anterior of these has two branches, the posterior three. In Megalobatrachus this vessel is more obviously one trunk with many branches. These and other reasons (such as the at least general persistence of a pair of gill-slits) lead m e to dissent from those who would unite the American and Japanese Salamanders into one genus, Cryptobranchus. A sheet of membrane, quite tough in character, extends from the right lobe of the liver to the parietes, and arches over a section of the body-cavity. Into the pocket formed at the corner of this next to the lateral parietes opens the oviduct. The general relations of these various parts are shown in the accompanying sketch (text-fig. 28). This cavity is entirely floored by the lung, and its boundary near the middle line of the body is the mesentery connecting the liver with the lung. On the right side, and below the shelter afforded by the transverse and horizontal |