HEART AND LUNGS OF MAMMAL. 137 



coat is the muscular coat; try to make out an inner 

 layer of circularly arranged fibres and an outer longi* 

 tudinal layer. 



4. Separate the gullet and windpipe and compare the 

 front and back surfaces of the latter ; cut across the 

 windpipe and make out the shape of the rings ot 

 cartilage. 



5. Observe the smooth rounded dorsal surfaces of the 

 lungs which were fitted against the ribs on each side 

 of the spinal column. 



6. Lay the lungs on the table, with their dorsal sur- 

 faces down, and with the point of the heart extending 

 away from you. The surface of the heart now upper- 

 most is its ventral surface, the side to your right is its 

 right side, and its left side is to your left. The point 

 of the heart is its apex, and the large end is its base. 



7. If the sac which surrounds the heart, the pericardium, 

 be not already cut away, note how easily the heart 

 moves about in it, and then slit it along its anterior 

 surface. Observe the pericardial fluid. 



8. Carefully compare the right and left sides of the 

 heart. Observe a groove running obliquely along the 

 anterior surface of the heart in which run blood-ves- 

 sels, often covered by fat. The part to the right of 

 this groove is the right ventricle ; the part to its left 

 is the left ventricle. Press the two sides and note 

 the difference in firmness. 



9. At the base of the heart, on each side, find an ear-like 

 appendage, with notched margins ; these are the right 

 and left auricles. 



10. Seize the apex of the heart and tip it up toward you. 

 Compare the front and back surfaces of the heart. 

 Compare the thickness of the heart from right to left 



