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 



Fia. 86. 



Transverse Sections through a Chick Embryo with 

 Twenty-one Mesoblastic Somites to shew the forma- 

 tion OF the Pericardial Cavity, A. being the Ante- 

 rior Section. 



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

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

 Guvieri. ao. aorta, mp. muscle-plate, mc. medullary cord. 



