106 OF ATTITUDE. 



7.* It is also easy to understand that its equilibrium will be 

 more stable in proportion to the extent of its base ; for then its 

 centre of gravity may be more displaced, without the vertical line 

 which passes through the centre of gravity, being carried beyond 

 the limits of this base of support. 



The more the centre of gravity is elevated above the base of 

 support, the less firm on the contrary will be the equilibrium, foi 

 a smaller displacement from this point will then suffice to carrj 

 the vertical line, that descends from it, beyond the base of support 

 which soon causes the body to fall.] 



The term attitude is applied to any position of the body that is 

 permanent during any considerable time. 



80. The principal attitudes of man are : lying, sitting, and the 

 erect position on his feet, or standing. 



81. When a man is lying on his back or on his belly, all parts 

 of the body rest upon the earth : he is not then required to con- 

 tract any muscle to keep them in place, and his position unites in 

 the highest degree the two conditions of equilibrium, to wit; the 

 greatest possible extent of the base of lu/tpu t and the proximity 

 of the centre of gravity to this base. Hence the attitude of re- 

 pose is that from which it is most difficult to fall. 



82. In the sitting position the body rests upon the tuberosities 

 of the ischium or haunch bones ; the base of support is considera- 

 ble, since it is represented by the pelvis, the extent of which is in- 

 creased by the soft parts which cover it; this position also, next 

 to lying, offers the greatest solidity ; but it cannot be preserved 

 without muscular action. When the back is supported, the mus- 

 cles of the neck alone contract to preserve the head erect ; but if 

 the back is not supported (as when seated on a stool or a bench 

 for example) then the greater part of muscles on the back of the 

 trunk contract to prevent it from falling forward, and fatigue will 

 sooner or later result from this permanent action. 



83. When man is erect, the lower extremities sustain the body 

 and transmit to the earth the weight which they support. Con 

 sequently these limbs must not bend under the load, and must be 

 kept straight by the contraction of their extensor muscles. 



84. In this position the centre of gravity of the whole body 

 lies in the cavity of the pelvis, and the base of support is circurn- 



79. Why is a body firm in proportion to the extent of its base 7 

 80 What are t l 'e principal attitudes of man ? 



81. What position or attitude is preserved without muscular exertion? 



82. What muscles are exerted to preserve the sitting position ? 



83. What supports the body when man is erect? 



81. Wh re is the centre of gravity in the erect position ? Where is th* 

 base of support in the erect position ? 



