260 MANUAL OF PHYSIOLOGY. 



7. The pulmonary arteries (P. A.) press steadily upon the 

 blood and force it through the following, viz. : 



8. Small pulmonary arterioles (P. a.) which regulate the flow 

 into the capillaries. 



FIG. 113. 



Interior of Bight Auricle and Ventricle exposed by the removal of a part of their 

 walla. (Allen Thomson.)!. Superior vena cava. 2. Inferior vena cava. 2'. Hepatic 

 veins. 3, 3', 3". Inner wall of right auricle. 4, 4. Cavity of right ventricle. 4'. Papillary 

 muscle. 5, 5', 5". Flaps of tricuspid valve. 6. Pulmonary artery, in the wall of which 

 a window has been cut. 7. Placed on aorta is near the ductus arteriosus. 



9. The pulmonary capillaries (P. C.), where the blood is ex- 

 posed to the air, and undergoes active gas interchange. 



10. The pulmonary veins (P. V.), carrying the blood to the 

 left heart, and thus completing the circuit. 



