RESPIRA TION. 



53 



lungs may be substituted in the place of the balloon) to 

 the inner end of one piece of the glass tubing. Slip a 

 piece of rubber tubing three inches long over the outer 

 end of the other piece of glass tubing, and put the pinch- 

 cock on the rubber tubing. 



d. Partially exhaust the air from the bottle by sucking 

 through the rubber tubing, then close the pinch-cock. 

 This represents the condition in the thorax. 



e. Lower and raise the rubber diaphragm. Notice what 

 occurs and explain. 



II. THE DORSO-VENTRAL ENLARGEMENT OF THE 

 THORAX. 



Apparatus. Six pieces of cardboard or thin wood six inches long 

 and one inch wide. Two light rubber bands. Eight fasteners. 

 Four hooks. 



Fasten four parallel pieces of stiff cardboard at right 

 angles to two parallel bars so that they may be moved at 

 the fastenings. Place the hooks at 1, 2, 

 3, and 4 (Fig. 8) so that a line connecting 

 1 and 2 shall be at right angles to one 

 connecting 3 and 4. The elastic bands 

 shall be so short as to be put on the 

 stretch when placed over the hooks. The 

 longest piece represents the spinal col- 

 umn. The shortest piece represents the 

 sternum. The three or four pieces of 

 equal length, movable at either end, rep- 

 resent the ribs. The band 12, running obliquely down- 

 ward and forward, represents the external intercostal 



FIG. 8. A model to 

 show the dorso-ven- 

 tral enlargement of 

 the thorax. 



