THK LUNGS AND RESPIRATION. 209 



seen that the breast bone is connected with numerous pairs 

 of ribs which extend from the breast bone backwards and up- 

 wards. If, now, by proper muscles these ribs are raised, 

 the result will be that not only the breast bone will move 

 upward, but also forward. This may readily be exemplified 

 by joining both hands and letting them rest in front on the 

 pelvic region. If, now, the arms be raised up, not only are the 

 hands raised, but they are also pushed away from the body, 

 and when the arms are extended directly forward may be 

 almost two feet or more from the trunk, whereas in their 

 original position they rested immediately against it. 



A third enlargement of the chest is the lateral enlarge- 

 ment. This is brought about by the fact that not only are 

 the ribs lifted up, but they rotate outward. This enlarge- 

 ment may be illustrated in the example of the raising of the 

 folded hands also. If, in addition to the lifting of the 

 hands, as in the preceding illustration, the arms be some- 

 what bent and rotated outwards, it is at once apparent that 

 the lateral diameter is increased. 



While an inspiration results from an enlargement of the 

 chest, an expiration is due to a contraction of the chest. 

 Under ordinary circumstances an expiration is a passive 

 process. We expand the chest and take air in by an active 

 contraction of muscles, but we expire by simply relaxing 

 the muscles and letting the chest drop back to its natural 

 dimensions. Sometimes, however, the expiration may be- 

 come forced. This may be accomplished in three different 

 ways, which are the exact opposites of those given for en- 

 larging the chest. That is, the diaphragm may be pushed 

 up further into the chest and become more dome-shaped 

 than before. This is done by contracting the abdominal 

 muscles and so pressing the stomach, liver and intestines 

 up against the diaphragm, and in this way lifting it up. 

 Or, a forced expiration may result from pulling the breast 

 bone downwards and rotating the ribs inward. 



It is unnecessary to say that generally all three ways are 

 used at the same time, although the breathing of men is 

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