BODY CAVITIES, DIAPHRAGM AND MESENTERIES 



i8s 



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 11 mm. 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. 



Pleuro-pericardial membrane Phrenic nerve 



Pleural cavity 



Pleuro- 

 peritoneal 

 membrane 



Mesonephros 



Fig. 194. — Reconstruction of an 11 nun. human embryo to show the same structures as in Fig. 193 (after 



Mall). X 14. 



By way of the pleuro-pericardial membranes the phrenic nerves course to the 

 septum transversum (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 (Lewis) (Fig. 196). 

 Between the free margins of the membranes and the mesentery a temporary open- 

 ing is left on each side, through which the pleural and peritoneal cavities com- 

 municate (Figs. 194 and 200). 



