48s MR. G. W. BUTLER ON THE [June 14, 



adults of all Snakes ; and this, not merely because I have not in a 

 number of cases been able to satisfy myself as to its presence by 

 dissection, but also because in Elaphis quadrilineatus, of which I 

 obtained some advanced embryos, I find, by serial sections, that it 

 is almost totally obliterated while still within the egg. 



If this space is present, one may expect to find it as a small one 

 immediately on the right side of the stomach, and especially of the 

 hinder part thereof — in fact, lying between the gall-bladder and the 

 stomach and bounded behind by the pancreas. It will not in any 

 case extend caudad of the pancreas, and it may not reach quite so 

 far back as the anterior end of that organ in the adult. Anteriorly 

 it may, when specially well developed, extend forwards as a narrow 

 space on the right side of the stomach to a point a little anterior to 

 the posterior end of the right liver-lobe {Typhlops lumbricalis). 

 This omental space, in the Snakes which I have examined, is best 

 seen in Typhlops, Xenopeltis, and the Pythonidse ; it is also well 

 marked, though in a less degree conspicuous, in Compsosoma, Den- 

 drophis, and others, I could not distinctly m.ake it out in the forms 

 marked {b) and (c)in the list (p. 489). 



This " omental" space must not be confused with the "gastric " 

 space above described, which runs close to it but more to the left 

 side ; that, in its hinder region, usually distinctly wraps round the 

 left side of the pyloric part of the stomach, vrhile this omental space 

 is on its right side. 



believe, disguised, by the fenestration of the mesogastric and gastrohepatic 

 ligaments, in the Amphibia also. 



The word " omental" is somewhat ambiguous, and " lesser 'peritoneal cavity ," 

 though excellent for the Mammalia, is unsatisfactory in the case of Birds, 

 Crocodiles, and Snakes, where there is moi'e than one such cavity present. 



It may be explained, then, that the term " omental space " is here used to 

 include the whole space that corresponds to (a) the " Saccus omenti " of 

 Mammals (the sac enclosed by the recurved stomach and its attached membranes), 

 and (b) the " Eecessus superior sacci omenti " of His, which in embryos of 

 Mammals extends forwards into the pulmonary region, and is the right 

 " pulmohepatic recess " of my previous paper (5). In Lizards, Crocodiles, and 

 Birds this " recess " may be more important than the " saccus " itself. 



In the adults of most Lizards, of certain Chelonians (Thalassochelys), and 

 at any rate of certain Mammals, and in the embryonic stages of Crocodiles, 

 Snakes, and Birds, we find that this " omental space " communicates with the 

 right side of the peritoneal cavity by an aperture (very wide in many Lizards) 

 which is the " Foramen of Winslow." This " Foramen of Winslow " is bounded 

 postero-ventrally by the pancreas and tlie hepatic ducts, which run in the hinder 

 margin of the gastro- hepatic ligament, and antero-dorsally by the posterior vena 

 cava, which, in its course from the kidneys (or in an embryo from the Wolffian 

 bodies) to the liver, runs in what either is, or once was, the posterior margin of 

 a ligament attaching the right half of the liver to the dorsal body-wall. 



This " Foramen of Winslow " may persist as described, as in most Lizards 

 and some Chelonians ( Thalassochelys) and Mammals ; or it may become oblite- 

 rated, as in Amphisbtenians, certain Chelonians {Testudo and Emys), Snakes, 

 Crocodiles, and Birds (Gallus). 



In the latter case we have, as a result, an entirely closed peritoneal sac. 



