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PHYSIOLOGY FOR DENTAL STUDENTS. 



diameters, from above downwards by the contraction of the 

 diaphragm, and in the transverse diameter by the movement of 

 the ribs. 



THE PART PLAYED BY THE DIAPHRAGM. The diaphragm is a 

 circular sheet of muscle which divides the body cavity into two 

 compartments, the upper being the thorax, the lower the abdom- 



Fig. 30. Bering's apparatus for demonstrating the action of the respira- 

 tory pump. The thorax is represented by a bottle, the diaphragm by a sheet 

 of rubber forming its bottom, the trachea by a tube passing through the 

 cork, and the lungs by two thin rubber bags. A thin piece of rubber tubing 

 crosses the bottle. This represents the heart. The action of the diaphragm 

 pumps air in and out of the lungs and water through the heart. The lungs 

 and heart are thin rubber bags. (From Baird and Co.'s catalogue.) 



inal cavity. In the upper compartment are the lungs and heart 

 with the accompanying blood vessels and air passages. The ab- 

 dominal cavity contains the digestive organs and glands, as the 

 liver, kidneys, spleen and reproductive organs. The peripheral 

 edges of the diaphragm are attached to the lumbar vertebrae at 

 the back, to the lower border of the ribs on the sides, and to the 

 tip of the sternum in front. The muscular fibers radiate to- 



