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Show 488 MR. G. W. BUTLER ON THE [June 14, adults of all Snakes; and this, not merely because I have not in number of cases been able to satisfy myself as to its presence by dissection, but also because, in Elaphis quadrilineatus, of which I obtained some advanced embryos, I find, by serial sections, that it is almost totally obliterated while still within the egg. If this space is present, one may expect to find it as a small one immediately on the right side of the stomach, and especially of the hinder part thereof-in fact, lyiny between the gall-bladder and the stomach and bounded behind by the pancreas. It will not in any case extend caudad of the pancreas, and it may not reach quite so far back as the anterior end of that organ in the adult. Anteriorly it may, when specially well developed, extend forwards as a narrow space on the right side of the stomach to a point a little anterior to the posterior end of the right liver-lobe (Typhlops lumbricalis). This omental space, in the Snakes which I have examined, is best seen in Typhlops, Xenopeltis, and the Pythonidee; it is also well marked, though in a less degree conspicuous, in Compsosoma, Den-drophis, and others. I could not distinctly make it out in the forms marked (b) and (c)in the list (p. 489). This " omental" space must not be confused with the "gastric " space above described, which runs close to it but more to the left side; that, in its hinder region, usually distinctly wraps round the left side of the pyloric part of the stomach, while this omental space is on its right side. believe, disguised, by tbe fenestration of the mesogastric and gastrohepatic ligaments, in the Amphibia also. The word " omental" is somewhat ambiguous, and " lesser peritoneal cavity," though excellent for the Mammalia, is unsatisfactory in the case of Birds, Crocodiles, and Snakes, where there is more than one such cavity present. It may be explained, then, that the term " omental space " is here used to include the whole space that corresponds to (a) the " Saccus omenti" of Mammals (the sac enclosed by the recurved stomach and its attached membranes), and (b) the " Eecessus superior sacci omenti" of His, which in embryos of Mammals extends forwards into the pulmonary region, and is the right " pulmohepatic recess " of m y previous paper (5). In Lizards, Crocodiles, and Birds this " recess " may be more important than the " saccus " itself. In the adults of most Lizards, of certain Chelonians (Thalassochelys), and at any rate of certain Mammals, and in the embryonic stages of Crocodiles, Snakes, and Birds, we find that this " omental space" communicates with the right side of the peritoneal cavity by an aperture (very wide in many Lizards) which is the " Foramen of Winslow." This " Foramen of Winslow " is bounded postero-ventrally by the pancreas and the hepatic ducts, which run in the hinder margin of the gastro-hepatic ligament, and antero-dorsally by the posterior vena cava, which, in its course from the kidneys (or in an embryo from the Wolffian bodies) to the liver, runs in what either is, or once was, the posterior margin of a ligament attaching the right half of the liver to the dorsal body-wall. This " Foramen of Winslow" may persist as described, as in most Lizards and some Chelonians (Thalassochelys) and Mammals; or it m a y become obliterated, as in Amphisbtenians, certain Chelonians (Testudo and Emys), Snakes, Crocodiles, and Birds (Gallus). In the latter case we have, as a result, an entirely closed peritoneal sac. |
