1892.] BODY-CAVITY IN SNAKES. 497 



large measure along lines followed in eiFecting 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) posthepntic 



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) 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 Oisterna magna. 



c.w Wolffian body. 



/. Developing fat-body pr oj ecting into circumadiposal 



lymph-space. 



g.bl Gall-bladder. 



oesoph CEsophagus. 



P Signifies a part of the pleuroperitoneal cavity, thus : — 



P^ That part of peritoneal cavity which later forms the 



closed gastric space. 



pi That part which will form a liver-sac. 



P.lr-liver-sac Is the already closed left liver-sac. 



P 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. 



JJmb Umbilical stalk. 



VM 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 (c?) of Elaphis quadrilineatus, 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. 'Simbx^o {S^) oi ElapMs quadrilineatus, 15 cm. long. Nat. size. Out- 

 line sketch of an artificially straightened embryo for comparison 

 with A. 



Fig. 1^. Transverse section of ElapMs embryo, of the same size as fig. A, tln-ough 

 the ventricle of the heart ( X 14). 



