136 Practical Zoology. 



it as it arches over the left bronchus and runs down between 

 the two lungs by the side of the gullet. Clear away any fat 

 or other tissue adhering to it. 



15. From the arch of the aorta arise the branches running 

 to the head and fore limbs. 



1 6. In the same way trace and clear the pulmonary artery. 



17. When the fork of the pulmonary artery has been reached, 

 lay the heart and lungs on their ventral surfaces, with the 

 posterior end toward you ; turn the windpipe back toward you, 

 and with the scalpel handle trace the branches of the pulmonary 

 artery into the lungs. Cut them off close to the lungs. 



1 8. Keeping the parts in the same position, trace the pul- 

 monary veins. These are to be found on the ventral side of 

 the bronchi ; their general outlines may be shown by inflating 

 as follows : Cut off the first branch of the aorta as close as 

 possible to the arch. Insert one blade of the scissors in this 

 opening, pointing away from the heart, and make a slit two 

 inches long. Insert a cork toward the heart. It should fit 

 snugly, so that air may not escape. For a pig's heart a cork 

 three fourths of an inch in diameter at its larger end is 

 about right. Make a very small hole in the tip of the left 

 auricle, insert the blowpipe, holding firmly around it, and 

 inflate. This should distend the left auricle and the pulmonary 

 veins. With the handle of the scalpel scrape away fat or con- 

 nective tissue that covers them, and trace them to the left 

 auricle. How many are there ? Cut off the left bronchus 

 close to the lung, and turn the windpipe to the right. Clear 

 the pulmonary veins from any tissue that lies under them. 

 Turn now to the ventral surface of the heart ; lift the ventral 

 margin of the flap of the left auricle, and with scissors cut into 

 the left auricle through the bottom of the groove between the left 

 auricle and the left ventricle. Make a slit an inch long, follow- 

 ing the groove. Pass a probe into the opening, then directly 

 across the cavity of the auricle, to the dorsal wall of the 

 auricle. Here are the entrances of the veins from the right 



