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.) We 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 v^ell as in Snakes, we get the left, anterior, 

 portion of the posthepatic peritoneal cavity shut off as a 

 gastric space, leaving tlie 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) On the other hand, while there are points about the oblitera- 

 tion 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. 



ao Dorsal aorta. 



cist, mag Cisterna magna. 



c.w Wolffian body. 



y Developing fat-body projecting into circumadiposal 



lymph-space. 



gM Gall-bladder. 



oesoph Oesophagus. 



P Signifies apart of the pleuroperitoneal cavity, thus: — 



-P" That part of peritoneal cavity which later forms the 



closed gastric space. 



-P ' That part which will form a liver-sac. 



P.l-liver-sac Is the already closed lelt liver-sac. 



P^ 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 (c5') of Elaphis qiiadrilineatus, 11 cm. long. Nat. size. Out- 

 line sketch, to show the relations and proportional development of 

 the lung, liver, and other parts indicated. [The embryos were curled 

 round in the 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.J 



Fig. B. Embryo ( $ ) of Elaphis quadrilineatus, 15 cm. long. Nat. size. Out- 

 line sketch of an artificially straightened embryo for comparison 

 with A. 



Fig. l'^. Transverse section of Elaphis embryo, of the same size as fig. A, through 

 the ventricle of the heart (Xl4:). 



