1895.] AJJTATOMT OF PIPA AMBEICAITA. 829 



could find no trace of any membrane until about Lalfway 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 mesentei'ies 

 already spoken of. In the anterior part of the abdominal region 

 there is thus a tent-like cavity which might be mistaken — particu- 

 larly in the male, where it ends abruptly posteriorly — for a peri- 

 cardium. 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 com- 

 mencing 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 ccelom 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. Gr. 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 sepa- 

 rated by an interval from the peritoneum covering the muscles of the parietes, 

 and anteriorly there is a vertical transverse septum joining them. 



Peoo. Zool. Soc— 1895, No. LIII. 53 



