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Show 1895.] ANATOMY OP PIPA AMERICANA. 829 could find no trace of any membrane until about halfway between the end of the abdominal cavity and the edge of the sternum. At this point where the membrane began the vein bifurcates. In the female frog the bifurcation of the abdominal vein coincides with the commencement of the fixed attachment of the mesenteries already spoken of. In the anterior part of the abdominal region there is thus a tent-like cavity which might be mistaken-particularly in the male, where it ends abruptly posteriorly-for a pericardium. In this cavity lies the heart, with its closely adherent pericardium. The abdominal vein lies inside the " tent," being here and there only loosely fastened to its walls. Where the abdominal vein bifurcates, which it does quite half an inch behind the edge of the liver, the cavity of the tent increases in depth vertically and its roof becomes attached to the stomach and commencing intestine, forming the ventral mesentery of the same. This cavity is an exaggeration of a corresponding arrangement in the frog. § The Diaphragm. I have already made use of the word " diaphragm " in describing the attachment of the liver. The liver is attached anteriorly on both sides of the body to a membranous wall which is continuous with the suspensory ligament of the abdominal veins and appears to limit the body-cavity anteriorly. To this is also attached the lung, and on the left side of the body in both sexes a deep pocket is formed behind the lung owing to the angle at which the two membranes join. This is slightly marked on the right side. Where the transverse vertical dissepiment is cut through it is seen not to mark the anterior boundary of the body-cavity. In front of it lie two cavities of considerable size, separated from each other by another vertical septum and from their fellows by the oesophagus. These cavities are suggestive of the water-tight compartments of a man-of-war. Whether they are true coelom or not I am unable to say. The septum to which the lung and the liver are attached is continuous with what I presume to be the dorsal peritoneum, or at least a portion of it. This membrane is tough and strong, and can readily be raised from the parietes. Anteriorly it is perforated by the two halves of the dorsal aorta, which lie perfectly freely in the space between the membrane and the parietes,being quite unattached to either. The anterior half of the cavity thus exposed by raising the tough peritoneal membrane is not floored (or rather roofed) by the muscles ; these are covered by ' a delicate semitransparent 1 It is possibly comparable to what Mr. G. W. Butler has described (P. Z. S. 1889, p. 445) in the Bird. Development appears to show that the oblique septum in the Fowl is one structure with the aponeurosis covering the lungs, it having been blown away from it, to use Mr. Butler's phraseology, by the intermediate air-sacs. But septa remain connecting the two layers and separating the air-sacs. So, in Pipa, the peritoneum lying immediately behind the lung is separated by an interval from the peritoneum covering the muscles of the parietes, and anteriorly there is a vertical transverse septum joining them. PROC. ZOOL. Soc-1895, No. LIII. 53 |
