270 



FRANKLIN P. MALL 



is still a free communication between the right ostium, with the 

 right ventricle and the vestibule of the aorta. The interventricu- 

 lar foramen is somewhat smaller in No. 175 (13 mm.) which is 

 cut in a more fortunate plane to illustrate this point than the 



Fig. 13 Sagittal section. Embryo 14mm. long (Xo. 144). X 40. 



Fig. 14 Coronal section. Embryo 17.2 mm. long (No. 424). X 24. 



other two embryos (fig. 12). The opening is gradually becoming 

 smaller in the following embryos in the order of their enumera- 

 tion, No. 423 (15.2), 144 (14, fig. 13), 424 (17, fig. 14). In 390 

 (15.5) it is uncertain whether it is closed or not, in 409 (16) it is 



