210 THE DEVELOPMENT OF THE CHICK 
At the stage of seventy-two hours, then, the pleural, pericar- 
dial and peritoneal divisions of the body-cavity are indicated, 
but all are in communication. The pleural cavities connect 
with the peritoneal cavity posteriorly, and with the pericardial 
cavity anteriorly in front of the lateral mesocardia (Figs. 118, 
119, 120); and the pericardial cavity communicates with the 
St. yey 
S-Qm ._ 
Viumb-. 
Lire ——<T 
Fia. 120. — Transverse section of the same embryo immediately 
behind the lateral mesocardia. 
ant. hep. Div., Anterior hepatic diverticulum. Duod., Duo- 
denum. End’e., Endoeardium. D.V., Ductus venosus. My’e., 
Myocardium. Pl. m’s’g., Plica mesogastrica. S-am., Sero-am- 
niotie connection. ven. r., l., Right and left limbs of the ven- 
tricle. V. umb., Umbilical vein. 
peritoneal cavity beneath the lateral mesocardia around the 
roots of the vitelline veins (sides of the anterior intestinal portal). 
Thus the ducts of Cuvier and the vitelline veins are the agencies 
that introduce the separation of the body-cavities. 
The tail-fold forms blind caelomic pockets in the region of 
the hind-gut, which end in the region of the thirty-third somite. 
(Cf. Fig. 81.) 
