194 



THE ENTODERMAL CANAL AND ITS DERIVATIVES 



septum transversum is carried caudally more rapidly than its ventral portion 

 and its ventral surface becomes its dorsal side (Figs. 186 and 187). The pleuro- 

 peritoneal membrane is carried caudad with the septum transversum until the 

 lung lies in the angle between the pleuro-peritoneal and pleuro-pericardial mem- 

 branes and is included within the spherical triangle which has been described 

 above (Fig. 187). 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. 187 and 188). In n mm. embryos the pleuro-pericardial 

 membranes have fused completely on each side with the median walls of the pleural 



Pleural 

 cavity 



Mesoderm of left lunq&ud 

 Pericardial ca.vify 



Pleura -peritoneal 

 tnembrane. 

 Phrenic nerve 



— Septum transversum 



falciform 

 ligament 



Fig. 188. — Transverse section through a 10 mm. human embryo showing the pleuro-pericardial mem- 

 brane separating the pericardium from the pleural cavities. X 33. 



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 

 transversum (Fig. 187). 



The pleuro-peritoneal membranes are continued dorsally and caudally along 

 the mesonephric folds; ventrally and caudally they become on the liver the 

 dorsal pillars of the diaphragm or coronary appendages (Lewis) (Fig. 189). Be- 

 tween the free margins of the membranes and the mesentery an opening is left 

 on each side, through which the pleural and peritoneal cavities communicate 

 (Figs. 187 and 193). 



