208 THE DEVELOPMENT OF THE CHICK 
instead of in front of them as before. Therefore in cross-sections, 
in front of the lateral mesocardia, the pleural grooves appear as 
dorsal projections of the parietal cavity, separated from one 
another in the middle line by the caesophagus (Fig. 118). 
The relations of the three divisions of the embryonic body- 
cavity thus established may be described as follows: the parietal 
cavity contains the heart, and is therefore the prospective peri- 
Fic. 118. — Transverse section of an embryo of 385s, imme- 
diately in front of the lateral mesocardia. 
Ao., Aorta. Atr., Atrium. B.a., Bulbus arteriosus. D.C. 
r., and l., Right and left duets of Cuvier. Lg., Lung. m’s’e. 
dors., Dorsal mesocardium. m’s’t. dors., Dorsal mesentery. 
P.C., Pericardial cavity. pl. gr., Pleural groove. Ree. pul. 
ent., Recessus pulmo-entericus. 5. V., Sinus venosus. 
cardial cavity. It is not, however, a closed cavity, but ecommuni- 
cates in front of the lateral mesocardia with the pleural grooves 
(Fig. 118), and by way of the latter above the lateral mesocardia 
with the peritoneal cavity (Figs. 119 and 120); a second communi- 
cation of the parietal cavity with the peritoneal cavity is beneath 
the lateral mesocardia around the sides of the anterior intestinal 
portal, now being converted into the septum transversum (cf. 
