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Show 1888.] ANATOMY OF THE LACERTILIA. 103 statements in this way, unless, indeed, the last half of the sentence from Hoffmann, quoted above, may be held to imply that the lungs are shut off from the abdominal cavity by a membranous partition. I should myself consider that these words only refer to the reflected layer of peritoneum which covers each lung ; this is, of course, quite a different thing from the horizontal membrane in Varanus, which shuts off both lungs from the abdominal cavity. I find, however, in an account of the dissection of a Monitor published in the very first volume of the ' Proceedings' ' of this Society, by Dr. Martin, a couple of sentences which in all probability do refer to this structure, which, so far as m y experience goes, is so highly characteristic of the Monitor Lizards and of that group only. The author writes : " the chest is divided from the abdomen by a partial membranous diaphragm attached to the parietes of the abdomen by numerous strings or filaments the liver lies in the abdominal cavity just below the diaphragm." There is, however, no further remark concerning the structure in question; it is not emphasized as a peculiarity of the Monitor nor is it compared in any way with what I believe to be an homologous structure in the Crocodilia. This horizontal septum closely resembles a structure in the Crocodilia (fig. 3) which bas been described by Prof. Huxley2 as well as by others : 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 envelopes 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 stomach and the two lobes of the liver ; the lungs are thus shut off from the abdominal cavity ; this membrane bears on tbe 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 lie 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 several 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, a resemblance which is, perhaps, a little unexpected. There has never, so far as I am aware, been any doubt as to the thoroughly Lacertilian nature of the Varanidae ; in all the schemes of classifica- » P. Z. S. 1831, p. 138. 3 P. Z. S. 1882, p. 568. |
