THE GENERAL STRUCTURE. 139 



down The mere adjustment therefore of weight and press- 

 urC; which may be the same the moment after death as the 

 moment before, does not support the cohmm. In cases also 

 of extreme w^eakness, the patient cannot stand upright. 

 Secondly, that these actions are only in a small degree vol- 

 untary. A man is seldom conscious of his voluntary powers 

 in keeping himself upon his legs. A child learniug to walk 

 is the greatest posture-master in the world ; but art, if it 

 may be so called, sinks into habit, and he is soon able to 

 poise himself in a great variety of attitudes, without being 

 sensible either of caution or efibrt. But still there must be 

 an aptitude of parts, upon which habit can thus attach — a 

 previous capacity of motions which the animal is thus taught 

 to exercise ; and the facility with which this exercise is 

 acquired, forms one object of our admiration. What parts 

 are principally employed, or in what manner each contributes 

 to its office, is, as has already been confessed, difficult to 

 explain. Perhaps the obscure motion of the bones of the feet 

 may have their share in this eflect. They are put in action 

 by every slip or vacillation of the body, and seem to assist in 

 restoring its balance. Certain it is, that this circumstance 

 in the structure of the foot, namely, its being composed of 

 many small bones, apphed to and articulating with one an- 

 other by diversely shaped surfaces, instead of being made of 

 one piece, like the last of a shoe, is very remarkable. 



I suppose also, that it would be difficult to stand firmly 

 upon stilts or wooden legs, though their base exactly imita- 

 ted the figure and dimensions of the sole of the foot. The 

 alternation of the joints, the knee-joint bending backward, 

 the hip-joint forward ; the flexibility, in every direction, of 

 the spine, especially in the loins and neck, appear to be of 

 great moment in preserving the equilibrium of the body. 

 With respect to this last circumstance, it is observable that 

 the vertebra? are so confined by ligaments as to allow no 

 more slipping upon their bases than what is just sufficient to 

 break the shock which any violent motion may occasion to 



