CHAPTER XI. 



MOVEMENTS OF EXPIRATION. 



Influence of the elasticity of the pulmonary structure and walls of the chest 

 Muscles of expiration Internal intercostals Infra-costales Triangularis ster- 

 ni Action of the abdominal muscles in expiration Types of respiration 

 Abdominal type Inferior costal type Superior costal type Frequency of the 

 respiratory movements Relations of inspiration and expiration to each other 

 The respiratory sounds Coughing Sneezing Sighing Yawning Laugh- 

 ing Sobbing Hiccough Capacity of the lungs and the quantity of air 

 changed in the respiratory acts Residual air Reserve air Tidal, or breathing 

 air Complemental air Extreme breathing capacity Relations in volume of 

 the expired to the inspired air Diffusion of air in the lungs. 



THE air is expelled from the lungs, in ordinary expiration, 

 by a simple and comparatively passive process. The lungs 

 contain a great number of elastic fibres surrounding the air- 

 cells and the smallest ramifications of the bronchial tubes, 

 which give them great elasticity. We can form an idea of 

 the extent of elasticity of these organs, by simply removing 

 them from the chest, when they collapse and become many 

 times smaller than the cavity which they before completely 

 filled. The thoracic walls are also very elastic, particularly 

 in young persons. After the muscles which increase the 

 capacity of the thorax cease their action, the elasticity of the 

 costal cartilages and the tonicity of muscles which have been 

 put on the stretch, will restore the chest to what we may call 

 its passive-dimensions. This elasticity is likewise capable of 

 acting as an inspiratory force when the chest has been com- 



