STRUCTURE OF THE HEART. 59 



fat or connective 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 in the groove between the left auricle 

 and the left ventricle. Make a slit an inch long, following 

 the groove. Pass a probe through 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 

 and left lungs. Use the finger as a probe, enlarging the open- 

 ing a little if necessary. Cut off the pulmonary veins near 

 the lungs, cautiously avoiding other blood tubes ; trim away 

 the pericardium. If the preceding work is interrupted at 

 about this point, wrap the heart first in wet, then in dry 

 paper ; write your name upon the wrapper, and keep the heart 

 in a cool place for later study. 



19. With the scissors slit down one bronchus through the 

 lung, noting its branches. Follow the outside of another 

 bronchus, tearing away the lung tissue with the scalpel handle. 



Structure and Action of the Heart. 1. Briefly re- 

 view : precaval vein ; postcaval vein ; right auricle ; right 

 ventricle ; pulmonary artery ; pulmonary veins ; left auricle ; 

 left ventricle ; aorta. Hold the heart suspended by the end 

 of the aorta, and dance it up and down to show the elasticity 

 of the aorta. Cut off the aorta where the slit was made at 

 the arch, and feel the inner surface. 



2. Eun a probe into the precaval vein, through the right 

 auricle, and out of the postcaval vein. Cut along the upper 

 side of the probe, and explore the cavity of the right auricle. 

 Feel the inside of the auricle and veins. Observe that the 

 cavity of the auricle extends farther into the heart than the 



