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Show 1892.] BODY-CAVITY IN SNAKES. 497 large measure along lines followed in effecting a similar subdivision in other groups of Sauropsida. Thus:- (i.) The omental space corresponds in all Sauropsida and it is a closed space, as in Snakes, in at any rate certain Birds, Crocodiles, and Chelonians. (ii.) W e may find in Sauropsida either a complete (Snakes, Crocodiles) or partial (Birds and Tupinambis) posthepatic septum across the body-cavity behind the liver. (iii.) In Crocodiles, as well as in Snakes, we get the left, anterior, portion of the posthepatic peritoneal cavity shut off as a gastric space, leaving the remainder as a closed intestino-genital space. As to each of the above-mentioned points, then, there seems to be a fairly close homology between Snakes and one or more of the other groups of Sauropsida. (5) O n the other hand, while there are points about the obliteration of the pleural cavity and the relations of the liver-sacs in Snakes which remind us of what occurs in Birds, there is perhaps no closer similarity in these respects between the two groups than between the " diaphragm " of Mammals and that of Birds. § IX.-EXPLANATION OF PLATE XXVIII. ew Dorsal aorta. cist, mag Cisterna magna. e.w Wolffian body. /. Developing fat-body proj ecting into circumadiposal lymph-space. g.bl Gall-bladder. oisoph Oesophagus. P Signifies a part of the pleuroperitoneal cavity, thus:- PB That part of peritoneal cavity which later forms the closed gastric space. Pl That part which will form a liver-sac. P.l-liver-sac Is the already closed left liver-sac. P v The pleural part of pleuroperitoneal cavity-destined to be obliterated. P° (in fig. 3) Narrow peritoneal tube connecting the right liver-sac and the posterior peritoneal cavity-destined to be obliterated. Umb Umbilical stalk. v.a Allantoic, or anterior abdominal vein. v.c.p Vena cava posterior. v.vp Vitelline-portal vein. *#' Connective tissue on free surface of lung. Fig. A. Embryo (J) of Elaphis quadrilineatus, 11 cm. long. Nat. size. Outline sketch, to show the relations and proportional development of tbe lung, liver, and other parts indicated. [The embryos were curled round in tbe eggs, and at this stage it would probably not be possible to straighten one to this degree. This is a rectified sketch of a partially straightened embryo.] Fig. B. Embryo ( $ ) of Elaphis quadrilineatus, 15 cm. long. Nat. size. Outline sketch of an artificially straightened embryo for comparison with A. Fig. 1A. Transverse section the ventricle of t hoef Ehelaarpth i(sX elm4b)r.y o, of the same size as fig. A, through |
