

DEVELOPMENT OF THE BODY CAVITIES 



73 



the dorsal end of the septum transversum the lung buds come to lie above the 

 septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity 

 (still, however, in free communication with one another) may be recognized; the 

 pericardial cavity opens into the pleural part. 



Left due of Cuvier Esopliagus Right duct of Cuvier 



m 



Omental bursa 



Stomach > n;': 



Meftoderm 



surrounding duct 



Pleuro-pericardial 



opening 

 Ridge growing across 



opening 



Dorsal mesentery 

 Peritoneal recess 



FIQ. 55. Upper part of celom of human embryo of 6.8 mm., seen from behind. (From model by Piper.) 



The ultimate separation of the permanent cavities from one another is effected 

 by the growth of a ridge of tissue on either side from the mesoderm surrounding 



Esophagus 



Aorta 



Pleural cavity 

 Lung 



Inferior vena cava 



Body wall 

 /,. Pericardium 



FIG. 56. Diagram of transverse section through rabbit embryo. (After Keith.) 



the duct of Cuvier (Figs. 54, 55). The front part of this ridge grows across and 

 obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- 

 peritoneal opening. 



With the continued growth of the lungs the pleural cavities are pushed forward 



