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surface than that of the thigh with the leg and knee-pan. Among the 

 orbicular articulations, no one has more points of contact than the joint 

 of the thigh bone to those of the pelvis. Professor Barthez says, that 

 when the body is erect, the head of the thigh bone and the acetabulum of 

 the os innominatum, which receives that bone, come in contact in a sur- 

 face of small extent. I am, on the contrary, of opinion, that in no pos- 

 sible case can the contact of two bones be more complete. The middle 

 line of direction of the upper part, the thigh bone, is then exactly perpen- 

 dicular to the surface of the comlyloid cavity, which embraces and 

 touches, in nearly every point, the almost spherical head of that bone. 



The cervix'on which the head of the bone is placed, by keeping the 

 thigh bone at a distance from the cavity of the pelvis, increases the ex- 

 tent of the space, in which the centre of gravity may vary without being 

 carried beyond its limits. 



CLXXXIV. The erect posture does not imply a perfect absence of 

 motion. It is on the contrary, accompanied by a staggering, which is 

 the more marked in proportion as the person has less strength and vig- 

 our. These perpetual oscillations, though but slightly distinct, in a man 

 who stands upright, depend on the incapacity of the extensors to keep 

 up a constant state of contraction, so that they become relaxed for a short 

 time, and the intervals of rest in the extensors are frequent, in proportion 

 to the weaker state of the subject. 



Some physiologists have given a very inaccurate idea of standing, by 

 making that attitude depend on a general effort of the muscles ; the ex- 

 tensors only are truly active. The flexors, far from assisting, tend, on 

 the contrary, to disturb the relation between the bones, necessary to ren- 

 der that state permanent. This explains, why standing is so much 

 more fatiguing than walking, in which, the extensors and flexors of the 

 limbs, are in alternate action and rest. 



It may be said, nevertheless, that to give the greater firmness to the 

 attitude, we sometimes contract, in a moderate degree, the flexors them- 

 selves ; then, that great part of the real force of the muscles, which acts 

 according to the direction of the levers which they are to set in motion 

 (CLXVI.) and which rs completely lost in the different motions which 

 they produce, is usefully employed in drawing together the articular ex- 

 tremities, in keeping their surfaces firmly applied to each other, and in 

 maintaining their exact superposition which is necessary to the erect 

 posture of the body. No one that I know of, had taken notice of this 

 employment of the greater portion of our muscular power, which was 

 thought completely lost by the unfavourable arrangement of our organs 

 of motion. The line, according to which all the parts of the body bear 

 on the plane which supports them, has much more tendency to fall for- 

 wards than backwards*; and falls forward are the most common and 

 the easiest. Thus, nature has directed, in the same direction, the mo- 

 tion of the hands, which we carry forward to break the force of our falls, 

 to prevent too violent shocks^ and to lessen their effect. At the same 

 time, she has provided means of protection towards the sides which the 



* This tendency is much less distinct in tall slender men. It is observed, that they, 

 for the most part, stoop in walking, less from the habit of bending- forward, than to pre- 

 vent the centre of gravity from falling- behind. Pregnant women, dropsical patients, 

 all persons who have much corpulence throw their body back, from an opposite and 

 easily understood reason. Copland. 



