VIII ] 



THE PERICARDIAL CAVITY. 



265 



matic side of the body cavity, dividing the body cavity 

 for a short distance in this region into a dorsal section, 

 {formed of a right and a left division) constituting the 

 true body cavity (Fig. 86 B, p.p), and a ventral section 

 (Fig. 86, B, p.c.), the pericardial cavity. The two parts 

 of the body cavity thus formed are at first in free com- 

 munication both in front of and behind this septum. The 



FIG. 86. 



TRANSVERSE SECTIONS THROUGH A CHICK EMBRYO WITH 

 TWENTY-ONE MESOBLASTIC SOMITES TO SHEW THE FORMA- 

 TION OP THE PERICARDIAL CAVITY, A. BEING THE ANTE- 

 RIOR SECTION. 



pp. body cavity, pc. pericardial cavity, al. alimentary cavity. 

 au. auricle, v. ventricle, sv. sinus venosus. dc. ductus 

 Cuvieri. ao. aorta, mp. muscle-plate, me. medullary cord 



