DISSECTION OF HEART AND LUNGS. 55 



surrounding tissues. All the other parts of the circulatory 

 system exist for the purpose of sending a continuous, slow, 

 and steady stream of blood through the capillaries. 



INTERNAL PROOFS OF THE CIRCULATION OF THE BLOOD. 



Heart and Lungs of a Pig. Get the butcher to save 

 the heart and lungs entire (the " pluck"), being careful not 

 to cut the lungs or the heart case. If a considerable number 

 are needed it is better not to depend on local butchers, but 

 to send to a large slaughtering-house in the nearest city. The 

 " plucks " should be thoroughly cooled before being shipped. 



1. Hold up the mass by the windpipe, with the heart away 

 from you. The end now uppermost is the anterior end, that 

 below is the posterior end ; the lung to your right is the right 

 lung ; the one to your left is the left lung ; the surface near- 

 est you is the dorsal surface, and that opposite is the ventral 

 surface. 



2. Observe the windpipe, or Trachea, with the stiff rings of 

 gristle, or Cartilage. The thick part of the anterior end is the 

 Larynx. 



3. Running along the dorsal surface of the windpipe is a 

 soft red tube, the Gullet,- or Esophagus. At about the middle 

 of the windpipe separate the gullet and windpipe for three 

 or four inches. Note that next to the gullet the windpipe is 

 soft and yielding where the gaps of the C-shaped cartilages 

 are filled with muscular and elastic tissue. Make a slit two 

 inches long in this soft membrane. 



4. Innate the lungs as follows: Take a wooden faucet, 

 slip the small end of the faucet into the slit just made in the 

 windpipe, and hold or tie firmly, but do not cut off either gul- 

 let or windpipe. Inflate through the spout, then shut off the 

 air ; if the lungs have not been punctured they should now 



