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 



Fig. 120. — Transverse section of the same embryo immediately 



behind the lateral mesocardia. 



ant. hep. Div., Anterior hepatic diverticulum. Duod., Duo- 

 denum. End 'c, Endocardium. D. V., Ductus venosus. My'c, 

 Myocardium. PI. m's'g., Plica mesogastrica. S-am., Sero-am- 

 niotic connection, ven. r., 1., 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 ccelomic pockets in the region of 

 the hind-gut, which end in the region of the thirty-third somite. 

 (Cf. Fig. 81.) 



