THE DEVELOPMENT OF THE HEART IN MAN. 
275 
the lumen into two portions, the position of the pulmonary and aortic valves, and 
the position of the interventricular foramen. The extent of the muscular coat is 
indicated, and the pulmonary and aortic valves are seen to lie at the distal extremity 
of the heart tube. These valves, and especially the pulmonary valve, are plump and 
well developed. 
Text-fig. 11. — Linear reconstruction (lateral) of portion of heart of embryo S4. 
As has been stated, there is an interventricular foramen of some size. Its position 
and exact boundaries are of considerable interest. It lies close to the basal portion 
of the ventricles, and it is between the two venous ostia. It is bounded dorsally by 
