112 



ANIMAL MECHANISM. 



alternately, while the muscles of the leg and the thigh, which 

 produce these movements, pass through alternations of con- 

 traction and relaxation. 



The intensity of the pressure of the feet on the ground 

 varies with the rapidity of walking and with the length of the 

 step. Besides this, the body passes through periodical oscil- 

 lations, the re-action of the impact of each foot on the ground; 

 and the different parts of the body are subject to this re-action 

 in various degrees. These oscillations are produced in diffe- 

 rent directions; some are vertical, others horizontal, so that 

 the trajectory which follows any point of a body is a very 

 complex curve. In addition to this, the body is inclined and 

 drawn up again at each movement of one of the legs ; it 

 revolves as on a pivot round the coxo-femoral articulation, at the 

 same time that it is slightly bent following the axis of the 

 vertebral column ; and, under the action of the lumbar muscles, 

 the pelvis moves and oscillates with a sort of rolling motion. 

 At the same time the anterior limbs, exerting an alternate 

 balancing power, lessen the influences which, at each instant, 

 tend to cause the body to deviate from the straight course 

 which it strives to maintain. 



All these acts have been analysed with much sagacity by 

 one of our pupils, Mons. G. Carlet,^ from whom we quote some 

 of the results which he has obtained. 



The motive force developed in walking, its pressure on the 

 ground in one direction, and its propelling effects on the mass 

 of the body on the other hand, are the three elements which 

 will at first occupy our attention. 



Motive force. This is found in the action of the exterior 

 muscles of the thigh, the leg, and the foot. The lower limb 

 forms, as a whole, a broken column, whose angles are rounded 

 off, and whose return to the perpendicular is effected by pres- 

 sure on the ground below, and on the body above. This is all 

 that we can say on this head, which, if treated more at length, 

 would require considerable amplifications. 



Pressure on the ground. This pressure, equal, as we have 

 before seen, to that in the opposite direction, which tends to 

 impel the body forward, must be studied in its duration ^ its 

 * G. Carlet, Etiule do la Marche. Aiiiinles des Sciences naturelles, 1872. 



