348 



PHYSIOLOGY. 



eral form of a dome. The peak, or convexity, of the dome points 

 upward. The student also knows that during contraction all mus- 

 cles shorten their fibers, to which law the diaphragm is no exception. 

 By its contraction the convexity of the dome is materially dimin- 

 ished, thereby producing more space and increasing the vertical diam- 

 eter. This helps very materially to produce a vacuum into which air 

 from outside of the body is pushed by atmospheric pressure. That 

 is, there occurs inspiration. 



Fig. 119. Schema of Respiratory Mechanism in Expiration. 

 (LAULANIE.) 



Th, Thoracic cavity having at its base an elastic membrane, having a cord 

 attached which makes traction in a vertical direction on the elastic membrane 

 which represents the diaphragm. The bottle has a cork with three openings. 

 *, Represents the trachea opening into a rubber balloon. Po, Representing a 

 lung, t", Connecting the interior of the bottle with a mercurial manometer, 

 t', A tube with a clamp to be put on when the rubber lung has been inflated; 

 it connects the space Th, which represents the pleural cavity. 



The diaphragm is supplied by the phrenic nerves. 



In addition to the diaphragm, inspiration is aided by the raising 

 of the ribs and sternum. Since the ribs are hinged posteriorly to 

 the vertebral column, it is their lateral and anterior portions which 

 possess the most motion; that is, their direction is slightly forward 

 and upward. 



