OCR Text |
Show 1889.] FAT-BODIES OF THE SAUROPSIDA. 607 lie in distinct spaces beneath the skin, separated from the abdominal cavity by a stout muscular tract, are not the homologues of the subperitoneal fat-bodies of the Monitors, but of subcutaneous fat-deposits occurring in the Sauropsida in addition to the subperitoneal (cf. p. 609). The fat-bodies of the Crocodiles that correspond to those of Lizards are more lateral than is usual in the latter group. Thus the membrane that is referred to by Beddard as being muscular in the Crocodile, according to the view here expressed represents, in the ventral region, a great part of the muscular body-wall. In the quotations given above the position of the kidneys relatively to the so-called " horizontal membrane " has been referred to. A reference to figs. 14 and 15 shows that in Monitor niloticus the hinder portion of the kidney projects well into the peritoneal cavity which contains the intestines and reproductive glands, and that the part in front of this lies as it were in the membrane in question, or between its peritoneal and parietal layers ; so that, though the anterior portions of the kidneys project outwards into the circumadiposal cavities, the membrane referred to does not exactly separate these from the reproductive glands. But, even if the whole of the kidney were shut out of the general intestinal cavity, this would, I think, neither be a point of special similarity to the Crocodiles nor have much morphological significance. W e find such a condition not only in the Crocodiles but in Chelonia (Emys, Testudo). In Snakes (cf. figs. 8, 9, 10), and in the Lizards themselves, the extent to which the kidneys project into the peritoneal cavity is variable, and the Amphisbgenidse are, so far as I know, unique in the freedom with which these organs hang into the peritoneal cavity. In birds, again, the kidneys, as opposed to the reproductive glands, are extra-peritoneal in position (cf. figs. 46 and47 of m y paper " On the Subdivision of the Body-cavity," Plate XLIX. above, p. 452). I think that the preceding points to the conclusion that the membrane which in Monitors is seen to cover the abdominal viscera when the body-wall is first cut into, must be regarded as the peritoneum, backed by the lining membrane of the space into which the fat-bodies project-that it, in fact, consists of the peritoneum together with another layer belonging to the body-wall. With regard to the term "horizontal" membrane or septum it seems to m e that it is used to comprise two things, which may with advantage be considered apart. There is, firstly, the membrane, referred to above, which divides the circumadiposal and peritoneal cavities. To this I would attach no particular morphological importance. It appears to me not to divide one part of the body-cavity proper from another, but to be, as Beddard (1, p. 100) seems fully to recognize, but a special development of a tract which occurs in other Lizards, correlated, as I would say, in Monitors with the greater extension of the circumadiposal spaces. In fact, in the separation of the membrane under discussion from the body-wall, the Monitors seem to be but following what is a line of weakness for Reptiles |