HEAET AND LUNGS OF MAMMAL. 139 



branches which supply the head and fore limbs. 

 Compare the branches, as here found, with those of 

 the rabbit's aorta, and of the human aorta as shown 

 by the cuts in any text-book of human anatomy and 

 physiology. 



15. Now trace the pulmonary artery and its two branches 

 as they subdivide to the right and left lungs. 



16. Follow the branches, the bronchi, of the windpipe to 

 the lungs. Follow one bronchus as it is distributed 

 through the lung. Observe the structure of the lung. 

 Cut a lung in two, and on the cut surface find the 

 flabby ends of the blood-vessels and the stiff ends of 

 the branches of the bronchi. With a probe trace the 

 latter back to the trachea. 



17. Try to distinguish the pulmonary veins; those from 

 the right lung run close along the right auricle on 

 their way to the left auricle. 



18. Cut the pulmonary arteries and veins near the lungs, 

 trim away the pericardium close to the heart, and 

 keep the heart in a cool place for further study. 



THE STRUCTURE AND ACTION OF THE HEART. 



1. Make three full-size drawings of the heart, front 

 view, back view, and side view, naming the parts and 

 blood-vessels as given above. 



2. With scissors slit down the vena cava superior, and 

 continue the cut across the back of the right auricle, 

 and for a short distance along the back of the vena 

 cava inferior. Explore the cavity of the right auricle. 

 Opposite the entrance of the vena cava inferior ob- 

 serve, in the red inner wall of the auricle, a rounded 

 depression, the fossa ovalis, across the bottom of 



