MECHANISM OF THE INFERIOR EXTREMITIES. 249 



into a full run, to prevent the body from being precipitated for- 

 wards to the ground. 



In jumping, the whole body is projected abruptly from the 

 ground, either in a vertical or oblique direction. 



In the first, the lower extremities are shortened by a general 

 flexure of their articulations, and, by a very sudden and simul- 

 taneous extension of them, the resistance of the ground causes 

 the whole frame to mount upwards, till its gravitation causes 

 the momentum to cease; it then descends on the same principle 

 with projectiles, generally. In the oblique leap, there is the 

 same flexion in all the articulations of the, lower extremities, 

 with the addition of an inclination, forwards, of the trunk. At 

 the moment when the limbs straighten themselves, the trunk is 

 projected, not only upwards, but forwards, owing to its inclina- 

 tion, and describes in its ascent and descent a parabola. In this 

 effort, the space traversed will be more considerable, if a pre- 

 vious horizontal momentum has been communicated to the trunk 

 by running several steps before the leap be made. 



The more oblique the leap is, the greater will be its extent, 

 to effect which the trunk must be inclined proportionably for- 

 wards. But, to obtain this inclination without falling, it is ne- 

 cessary for one of the lower extremities to be very much ad- 

 vanced at the moment of springing with the other, so as to con- 

 vert the motion into a very long step. With this position of 

 the lower extremities, a much longer space can be cleared than 

 if they were kept together.* 



* For a farther exposition of the principles of locomotion, see Joh. Alph. Bo- 

 relli de'Motu Animalium, 1710. Haller, Element Physiol. torn. iv. 1757. Bi- 

 chat, Anat. Descript. 1801. Barthez, Nouvelle Mechanique des Movemens de 

 1'Homme et des Animaux, 1798. 



