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Show 606 MR G. "W. BUTLER ON THE [DeC. 3, have been demonstrated, by a study of the development, everything points to the conclusion that the circumadiposal cavities are not homologous with any part of the peritoneal cavity proper of other types, but are altogether extra-peritoneal. Again: I do not consider that the membrane "which surrounds the abdominal viscera has its exact counterpart in Crocodilia and Aves " (1, p. 106), except in so far as it is a part of the body-wall. I take it that the " omentum " of Birds is represented in Monitors by the ligament which passes between the stomach and the hinder part of the liver antero-dorsally, and the dorsal face of Beddard's horizontal membrane postero-ventrally. In Monitors, however, as in most other Lizards, it has not acquired that extension in a transverse direction which conduces to the formation of a post-hepatic septum in Birds, Crocodiles, and the Teiidae (cf. my paper on the Subdivision of Body-cavity, above, p. 463). As to the Crocodiles, Beddard says (1, p. 103) that the horizontal membrane " closely resembles a structure in the Crocodilia which has been described by Prof. Huxley as well as by others." Beddard describes this structure as follows (the italics are mine) : - " This consists of a membrane, partly muscular, which is attached to the pubis and to the abdominal parietes behind, and in the median dorsal line to the backbone; it entirely envelops the coils of the intestines, so that they are not visible when the body-wall is cut through. Anteriorly this muscular expansion is attached to the fibrous compartments in which are lodged the two lobes of the liver ; the lungs are thus shut off from the abdominal cavity ; this membrane bears on the ventral surface the anterior abdominal veins : there is evidently a close similarity, so far, between the Crocodile and the Lizard; furthermore, in both animals the lateral regions of the membrane are connected with the lateral parietes by fibrous bands, and in both the fat-body lies outside of the membrane and outside of the abdominal cavity; the reproductive glands and the kidneys have a similar relation to the membrane in both types : in the Crocodile, as in the Lizard, the reproductive glands and the kidneys are separated by the membrane ; the former lies within, the latter without, the abdominal cavity. The only differences are that in the Crocodile the membrane is largely covered by muscular tissue, and that instead of simply passing over the liver and stomach, it becomes connected with special sheaths enveloping these organs. In these points the Crocodile, as Prof. Huxley has pointed out, resembles birds. The above considerations point, in my opinion, to an unmistakable resemblance between the Monitor Lizards and the higher Sauropsida." I have not at present observed a well-marked circumadiposal space round the subperitoneal fat-bodies of Crocodiles. But if, as I take it, the membranes above referred to in Monitors and Crocodiles are but the inner layers of the body-wall, they are doubtless homologous to a certain extent. I would add, however, with reference to the statement that the membrane in Crocodiles is " largely covered with muscular tissue," that (in m y opinion) the ventral fat-masses that |