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Show 3 1 8 MU. 11. H. BL'RNE ON THE [Apr. 18, Anteriorly, part of the ventral wall of tlie sac is attached to the dorsal surface of the left lobe of the liver in continuation of the mesentery of the transverse segment of the intestine and also to the lateral border of the liver. Otherwise, the anterior attachments of the sac were not very satisfactorily made out, but in all probability it merges with the peritoneum that lines the anterior end of the abdominal cavity. Another detail that does not appear so clearly in my notes as I could wish, is the exact point at which the oesophagus comes to lie entirely free within the sac. In Emys, although there is no similar sac of anything like these dimensions, there is an arrangement of the mesenteries that seems to represent it in a very much less developed condition. The oesophagus and stomach are suspended from the deep surface of the liver by a mesentery continuous with that which supports the transverse segment of the small intestine. This is no doubt comparable to the ventral wall of the sac in Dermochelys. But there is also a more dorsally placed and much looser sheet of mesentery that extends from the peritoneal lining of the anterior parts of the abdominal cavity to the stomach and lower end of the oesophagus. This, which I take to represent the dorsal wall of the sac, encloses between itself and the first-mentioned mesentery a deep pouch that lies behind the liver in the bend formed by the oesophagus, stomach, and intestine, but does not enclose within its cavity any free parts of the alimentary canal. The great development of this mesenteric sac in Dermochelys is most probably to be referred to the excessive length and bent form of the oesophagus and to the much complicated stomach. Ten inches beyond the point of entry of the bile-duct into the intestine wall, a free mesenterial fold appears upon the antisuspensory surface of the gut. The line of attachment of the fold is at first rather to one side of the mid-ventral line of the intestine, and in this part the fold is deep, and owing to the shortness of its free border compared with the length of its attachment forms a pouch in which are contained three coils of the gut. Beyond the region of the pouch the fold rapidly diminishes in depth and continues along the ventral surface of the intestine for some 16 inches. It terminates by branching off to either side to lose itself in the dorsal mesentery. In the angle between these two terminal folds is a small pigmented nodule, which may possibly be an extremely vestigial Meckel's diverticulum. I can find no indication of this ventral mesentery in Emys. Food. With the exception of the mouth, in which there was a small Teleostean fish, the only part of the alimentary canal that contained food was the tubular region of the stomach. In this part there were numerous tests of compound Tunicates, several small simple Ascidians, and a small piece of seaweed. |