474 MALL. [Vol. V. 



on either side of the lungs the pericardial cavity communicates 

 with the pleuro-peritoneal cavity by means of two openings, 

 each of which has a long diameter of 0.5 mm. and a short diameter 

 of o. 1 mm. The cavity now encircles the lungs, leaving, how- 

 ever, a dorsal and a ventral mesentery. More aboralwards a slit 

 passes about the liver, and one about the stomach, as shown in 

 Fig. 1. On the left side these two slits are quite smooth, and 



Fig. I. — Section through the foramen of Winslow of a human embryo 7 millime- 

 tres long. Enlarged 50 times. A., aorta; C. A., coeliac axis; S., stomach; C. D., 

 gastric diverticulum; F. IV., foramen of Winslow; P., portal vein; U., umbilical 

 vein; Z., liver. 



again run together on the aboral side of the liver. On the 

 right, however, instead of a slit we have a pocket, or diverticu- 

 lum, the cast of which is given in Fig. 2. The asymmetry of 

 the two sides corresponds with the shifting of the stomach, 

 and later the diverticulum forms the lesser peritoneal cavity. 1 

 Farther back the cavities on either side become symmetrical 

 again, and then communicate with each other on the ventral 

 side of the alimentary canal, as shown in Fig. 2, PI. XXX. 



1 Development of the Lesser Peritoneal Cavity, etc., Journal of ' Morph.^J '., No. 1. 



