Mammalia. 137 



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 in 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 into 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. i . Briefly review : 

 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. Run 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 

 notch between the auricle and ventricle. At the extreme left of 

 the right auricle is the mouth of the cardiac (coronary) vein, 

 which, running around between the left auricle and left ventricle, 

 brings blood from the ventral walls of the heart. Near the 

 mouth of this vein also empty the veins seen in the dorsal wall 

 of the heart. Pick out any clots that may be found. Slit the 

 anterior wall of the auricle, being careful not to cross the groove 

 between the auricle and ventricle, and note the muscular 

 columns within the appendage of the auricle. 



3. Cut away the whole of the appendage of the right auricle. 

 Remember that the pulmonary veins from the right lung run 

 very close to the right auricle, and be careful not to cut into 

 them. If necessary, pin down the flap of the left auricle, so 

 that water may not enter the left half of the heart in the next 



