No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 443 
The separation of the pleural from the pericardial cavity is 
dependent upon the complete development of the diaphragm. 
At first the septum transversum and the membrana reuniens are 


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Fic. 42. — Reconstruction of Embryo No. IX. Enlarged 17 times. S 7, septum transversum ; Z, 
liver; S, stomach; C, caecum; W, Wolffian body; A, kidney; 7-72, dorsal ganglia; 0, 
omphalomesenteric artery. The ventral mesentery of the liver is dotted, as it is only a thin 
membrane; S C, suprarenal capsule; A, point of communication between pleural and 
peritoneal cavities. 
on the ventral side of the pleural cavity, and both are still . 
located within the head. As the septum transversum descends 
into the body it is next located on the dorsal side of the heart. 
In other words, the dorsal end of the septum transversum has 
not moved as rapidly as the ventral end, and thus the whole 
