RESPIRATION 



LVIII. — Dissection of a Rat's Lungs. 



Apparatus. — Body of trhe rat used in Exs. XXXIII and LIII, 

 scalpel, glass tube of one-eighth inch diameter. 



Directions. — ^Remove the skin from the surface of the 

 ribs and throat. Examine carefully the muscles between 

 the ribs (intercostals). Seize the base of the breast bone and 

 move it up and down. Notice the motion of the inter- 

 costals during this process. 



Insert the glass tube in the top of the windpipe through 

 the throat opening, and blow gently through this tube. 

 Observe the motion of the ribs and the motion of the muscu- 

 lar diaphragm that forms the partition between the ab- 

 dominal and thoracic cavities. Press the diaphragm up with 

 the finger and note that air is forced out of the tube. 



Now cut the ribs where they join the breast bone, and press 

 them back to expose the organs of the cavity. Sketch the 

 position of the lungs and heart. Compare with Fig. 35, 

 page 76. Note the texture of the lungs and observe the 

 windpipe (trachea) with its cartilage rings. (These are nec- 

 essary to prevent collapse of the tube.) How is the windpipe 

 connected with the lungs? 



Carefully dissect out the lungs and windpipe and float 

 them in water. Cut them at the entrance of the windpipe 

 and trace out the bronchi and their branches. How do these 



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