The upper part of the body is slightly inclined forward; the head slightly thrown backward, to counteract the gravity forward: the breast is freely projected; the shoulders are steady, to give a fixed point to the auxiliary muscles of respiration: the upper parts of the arms are kept near the sides; the elbows are bent, and each forms an acute angle; the hands are shut, with the nails turned inwards; and the whole arms move but slightly, in order that the muscles of respiration on the chest may be as little as possible disturbed, and follow only the impulse communicated by other parts--(Plate IX. fig. 1). There exists, in fact, during the whole time of running, a strong and permanent contraction of the muscles of the shoulder and arm, which, though very violent, is less serviceable to the extended movements, than to keep the chest immoveable, toward which the arms are brought close, the flexors and adductors of which are especially contracted. ACTION IN RUNNING. At every step, the knees are stretched out; the legs kept as straight as possible; the feet almost graze the ground; the tread is neither with the mere balls of the toes, nor with the whole sole of the foot; and the spring is made rapidly from one foot to the other, so that they pass each other with great velocity--(Plate IX. fig. 2). But the abdominal members are not the only ones in motion, although it is in them that the greatest developement takes place. Throughout the whole time of running, a strong and permanent contraction of the muscles of the shoulder, arm, and forearm takes place: this, though very violent, is less for the purpose of aiding motion than of preserving the immobility of the thorax, which is pressed upon the whole thoracic member, whose flexors and adductors are strongly contracted. The degree of velocity, however, must be proportioned to the length of the steps. Too slow and long, as well as too quick and short, steps, may be equally injurious. [Illustration: _Plate IX_ _Page 38._ Running.] RESPIRATION.