i86 



THE ENTODERMAL CANAL AND THE BODY CAVITIES 



than its ventral portion, and its primary ventral surface becomes its dor- 

 sal side (Figs. 192 to 194). The pleuro-peritoneal membrane is carried 

 caudad with the septum transversum until the lung lies in the angle be- 

 tween the pleuro-peritoneal and pleuro-pericardial membranes and is 

 included within the spherical triangle which has been described above 

 (Fig. 194). During this rotation the dorsal end of the pleuro-pericardial 

 membrane lags behind and so takes up a position in a coronal plane nearly 

 at right angles to the septum transversum (Figs. 194 and 195). In 1 1 mm. 



Pleuro-pericardial membrane Phrenic nerve 



Septum transversum 



Pericardial cavity 



Pleuro- 

 peritoneal 

 membrane 



Mesonephros 



Stomach 



FIG. 194. Reconstruction of an n mm. human embryo, to show the same structures as in Fig. 

 193 at a later stage (after Mall). X 14. 



embryos the pleuro-pericardial membranes have fused completely on each 

 side with the median walls of the pleural canals and thus separate the 

 pericardium from the paired pleural cavities. By way of the pleuro- 

 pericardial membranes the phrenic nerves course to the septum transver- 

 sum (Fig. 194). 



The pleuro-peritoneal membranes are continuous dorsally and caudally 

 with the mesonephric folds; ventrally and caudally they fuse later with 

 the dorsal pillars of the diaphragm, or coronary appendages of the liver 



