18 Cincinnati Society of Natural History. 
the general peritoneal cavity, through a narrow slit about 
I-2 cm. in length — the pericardio-peritoneal foramen. (See 
Figs. VI, X, XIX, pcef). The direction of the slit is not 
quite longitudinal, but extends slightly outward anteriorly. 
The lower margin of the foramen is formed anteriorly by the 
fold extending upward from the liver (hepatic ligament) 
(See Fig. VI). Posteriorly, the slit borders on the lateral 
wall of the alimentary canal. The upper margin of the slit 
is formed posteriorly by the body wall and anteriorly by a 
reflection of the peritoneum from the wall. Through the 
pericardio-peritoneal foramen passes the supra-intestinal vein 
closely attached to.the lateral wall of the intestine. The 
anterior extremity of the right mesonephros extends through 
the foramen, projecting from the inner side of the roof. The 
floor of the outer chamber is formed anteriorly by the upper 
surface of the anterior lobe of the liver; posteriorly, by the 
fold extending from the upper surface of the lobe to the 
lower margin of the pericardial foramen. The roof of the 
outer chamber is in direct contact with the body wall. 
External to the portal heart, toward the anterior end of the 
chamber, the sight pronephros projects downward and out- 
ward into the cavity, pushing the pericardium before it. Just 
behind the pronephros, and above (outside) the pericardium, 
along the inner margin of the chamber, lies the anterior end 
of the mesonephros, which extends backward through the 
pericardial foramen, as described. In the posterior region 
the outer chamber lies against the right side of the intes- 
tinal wall. Along this wall a fold of the pericardium extends 
from the pericardial foramen to the posterior end of the 
portal heart. This fold encloses the sapra-intestinal vein. 
(See Fig. XIII.) 
The zzner chamber of the right pericardial cavity lies 
internal to the portal septum, and encloses the ventricle of 
the heart. It is much larger than the outer chamber, being 
of about the same length, but wider and deeper. The inner 
chamber is situated slightly ventral to the outer. Anteriorly, 
the chamber is about 34 cm. deep. Posteriorly, it becomes 
shallower and narrower, terminating just anterior to the gall 
bladder, and above the anterior lobe of the liver. On the 
left side the inner chamber forms a blind sac into which a 
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