POSTURES. 149 



less; the reason being of course the more advantageous 

 direction of traction by the biceps in the latter case. 



Experiment proves that the power with which a muscle 

 can contract is greatest at the commencement of its short- 

 ening, the very time at which, we have just seen, it works 

 at most mechanical disadvantage; in proportion as its force 

 becomes less the conditions become more favorable to it. 

 There is however, it is clear, nearly always a considerable 

 loss of power in the working of the skeletal muscles, 

 strength being sacrificed for variety, ease, rapidity, extent, 

 and elegance of movement. 



Postures. The term posture is applied to those posi- 

 tions of equilibrium of the Body which can be maintained 

 for some time; such as standing, sitting, or lying, com- 

 pared with leaping, running, or falling. In all postures 

 the condition of stability is that the vertical line drawn 

 through the centre of gravity of the Body shall fall within 

 the basis of support afforded by objects with which it is in 

 contact; and the security of the posture is proportionate to 

 the extent of this base, for the wider it is, the less is the 

 risk of the perpendicular through the centre of gravity fall- 

 ing outside of it on slight displacement. ,j 



The Erect Posture. This is pre-eminently character- 

 istic of man, his whole skeleton being modified with refer- 

 ence to it. Nevertheless the power of maintaining it is 

 only slowly learnt in the first years after birth, and for 

 a long while it is unsafe. And though finally we learn to 

 stand erect without conscious attention, the maintenance 

 of that posture always requires the co-operation of many 

 muscles, co-ordinated by the nervous system. The influ- 

 ence of the latter is shown by the fall which follows a 

 severe blow on the head, which may nevertheless have frac- 

 tured no bone and injured no muscle: the "concussion" of 

 the brain, as we say," stuns" the man, and until its effects 

 have passed off he cannot stand upright. In standing 

 with the arms straight by the sides and the feet together 

 the centre of gravity of the whole adult Body lies in the 

 articulation between the sacrum and the last lumbar verte- 

 bra, and the perpendicular drawn from it will reach the 



