. Applied anatomy and kinesiology. ndsternum. Observation shows that it lifts the ribs slightly butdepresses its own central tendon as its principal movement. Obser-vation also shows that it acts in unconscious breathing in unison THE DIAPHRAGM 215 with the intercostals or nearly so. As it descends it flattens andleaves more room in the chest, thus aiding the intercostals in enlarg-ing the chest. Duchenne considers it the most important of thebreathing muscles, since he found it to be the only muscle that canmaintain without much eftort a sufficient flow of air to supply thetissues when all ot
. Applied anatomy and kinesiology. ndsternum. Observation shows that it lifts the ribs slightly butdepresses its own central tendon as its principal movement. Obser-vation also shows that it acts in unconscious breathing in unison THE DIAPHRAGM 215 with the intercostals or nearly so. As it descends it flattens andleaves more room in the chest, thus aiding the intercostals in enlarg-ing the chest. Duchenne considers it the most important of thebreathing muscles, since he found it to be the only muscle that canmaintain without much eftort a sufficient flow of air to supply thetissues when all other muscles of inspiration have been lost. The relation of the diaphragm to the abdomen is important, aswell as its relation to the chest. When it descends it must of coursetake from the abdomen just as much room as it gives to the pushes the stomach, liver, and other abdominal organs before it,and since these organs are soft and pliable but not compressible,they crowd out against the abdominal wall. The soft and flexible. Fig. 130.—The diaphragm. (Gerrish.) abdominal wall gives way, expanding on the front and somewhatat the sides to make the needed room. If the abdominal wall isthick and strong it offers considerable resistance to the descent ofthe diaphragm, and this will increase the upward pull of the latteron the ribs. The diaphragm always has to force out the abdominalwall against the pressure of the atmosphere, which is considerable,but the breathing is more efficient when the abdominal walls arestrong and well muscled. Simultaneous contraction of the intercostals and diaphragmexpands the chest in all directions and thus produces inhalation;in quiet breathing this is the only muscular action taking placewith the exception of the muscles in the walls of the bronchial 216 BREATHING tubes, which are not of the same variety and not usually includedin studies of the muscular system. When the muscles of inspira-tion relax, the air is expelled by the elasticity of th
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