The Pedestrian's Record

58 the pedestrian's record. increased in all directions, so as to bring about the general expansion of those portions of the lungs which lie at the back of the chest and spine, and this is effected by the descent of the diaphragm and the elevation of the ribs. The latter are raised by the contraction of the external intercostal muscles, which are located between each rib ; during laboured breathing other and numerous muscles are brought into play ; in fact, all surrounding thechest, and even the arms ; for instance, the scaleni, are strongly contracted, soas to raise or at least give a very fixed support to the first and second ribs. In the same way the serratus posticus superior, which descends from the fixed spine in the lower cervical and upper dorsal regions to the second, third, fourth, and fifth ribs, by its contraction raises those ribs. In laboured breathing a function of the lower false ribs, not very noticeable in easy breathing, comes into play. They are depressed, retracted, and fixed, thereby giving increased support to the diaphragm, and directing the whole energies of that muscle to the vertical enlargement of the chest. In this way the serratus posticus inferior, which passes upward from the lumbar aponeusosis to the last four ribs, by depressing and fixing them, becomes an adjuvant in­ spiratory muscle. All these muscles may come into action during breathing, which, although deeper than usual, is not excessively laboured. When, however, the need for greater inspiratory efforts becomes neces­ sary, all muscles which can from a fixed point act in