766 



THE THORAX. 



tinuation of the pulmonary artery, and opens into the arch of the aorta, just 

 below the origin of the left subclavian artery ; arid so conducts the chief part 

 of the blood from the right ventricle into the descending aorta. When the 

 branches of the pulmonary artery have become larger relatively to the ductus 

 arteriosus, the latter is chiefly connected to the left pulmonary artery; and the 

 fibrous cord, which is all that remains of the ductus arteriosus in later life, will 

 be found to be attached to the root of that vessel. 



Fir. 421. Plan of the Foetal Circulation. 



MfnalJbac jff 



In this plan the figured arrows represent the kind of blood, as well as the direction which it 



takes in the vessels. Thus arterial blood is fijrured 3K> >; venous blood, > > ; 



mixed (arterial and venous blood), >3> >. 



