Mammalia. 



'35 



to the lungs ; its branches are the bronchi. How many bronchi 

 are there ? Here are often found small, oval, brownish masses, 

 the lymphatic glands, embedded in connective tissues. Scrape 

 these loose with the scalpel handle. 



9. Lay the lungs, on their dorsal surface, with the anterior 

 ends toward you. Note how easily the heart may be moved 

 about in its case, the pericardium. Slit the pericardium along its 

 ventral side, and note the smoothness of its lining and of the 

 surface of the heart. Observe the pericardial fluid. 



10. Carefully compare the right and left sides of the heart. 

 Running obliquely across the surface of the heart is a groove 

 in which are blood tubes, often covered with fat. The part at 

 the right of the groove is the right ventricle ; at the left is the 

 left ventricle. 



11. At the base (anterior end) of the heart on each side are 

 the right and left auricles. 



12. Tip up and toward you the apex of the heart. Compare 

 its width and thickness ; compare the ventral and dorsal surfaces 

 as to length, convexity, etc. Press the two ventricles, and com- 

 pare them in firmness. 



13. Turn the heart to the left, and examine the right auricle ; 

 find a large, flabby, red tube entering its anterior surface, the 

 precaval vein. Prick a small hole in it, and insert the blowpipe ; 

 hold firmly around the opening and inflate. This shows the 

 outline of the right auricle. Meanwhile, watch closely the dorsal 

 part of the auricle ; the postcaval vein should now be discovered 

 entering the auricle from the posterior region. Look for it out- 

 side, and on the dorsal side of the pericardium, where it runs 

 anteriorly from the diaphragm. 



14. Turn the heart to the right, and observe a large, light- 

 colored tube arising from the base of the right ventricle be- 

 tween the two auricles ; this is the pulmonary artery. Again 

 turn the heart to the left, and raise the right auricle ; find the 

 aorta arising from the center of the base of the heart. Care- 

 fully separate the aorta from the pulmonary artery, and trace 



