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TEXT-BOOK OF EMBRYOLOGY. 



from the body wall through the dorsal free edge of the septum transversum to 

 join the sinus venosus (Fig. 292). This free edge is pushed farther and 

 farther into the ductus pleuro-pericardiacus (Fig. 293) until it meets and fuses 



Dorsal mesentery 



Pleural cavity 



Lung 



Lateral mesocardium -- 



Pericardial cavity 



Lateral mesocardium 



l\'~" Dorsal mesocardium 

 1 -, Heart 



FIG. 294. View (in perspective) of the pericardial and pleural cavities of a human embryo 



of 7.5 mm. Kollmann. 



The arrow points through the opening which forms the communication between the pleural 

 and peritoneal cavities, and which is eventually closed by the pleuro-peritoneal membrane. 



with the mesentery or posterior mediastinum. This process thus produces a 

 septum between each pleural cavity and the pericardial cavity. 



The septum transversum early acquires still more complicated relations 



Lung g 



Pleuro-peritoneal membrane 



Mesentery of 

 inf. vena cava if 



Inferior vena cava --- 

 Mesonephros ^M 



Lung 



Pleuro-peritoneal membrane 

 Mesentery 



P'euro-peritoneal membrane 

 CEsophagus 



Dorsal mesogastrium 



FIG. 295. Ventral view (in perspective) of parts of the lungs, pleural cavities, peritoneal cavity, 

 and the pleuro-peritoneal membranes in a rat embryo. Ravn. 



from the fact that the liver grows into its caudal part (Fig. 292) . It may, for this 

 reason, be divided into a caudal part in which the liver is situated and which 

 furnishes the fibrous capsule (of Glisson) and the connective tissue of the liver, 

 and a cephalic part which may be called the primary diaphragm. These two 

 parts at first are not separate, the separation taking place secondarily. After 





