LOCOMOTION. 



611 



tissue, for abundant nourisliment, growth, and repair after in- 

 jury. 



We find in the body of mammals, including man, examples 

 of all three kinds of levers. It sometimes happens that there 

 is an apparent sacrifice of energy, the best leverage not being 

 exemplified ; but on closer examination it will be seen that the 

 weight must either be moved with nice precision or through 

 large distances, and these objects can not be accomplished al- 

 ways by the arrangements that would simply furnish -the most 

 powerful lever. This is illustrated by the action of the biceps 

 on the forearm. 



It is to be remembered that, while the flexors and extensors 

 of a limb act in a certain degree the opposite of one another, 



Fig. 452.— Skelotnn 'of deer. The bones in the extremities of this the fleetest of qnad- 

 rnpeds are inclined very ol)liquely toward each other and toward tlie scapular and 

 iliac bones. This arrangement increases the leverage of the muscular system and 

 confers great rapidity on the moving parts. ' It augments elasticity, diminishes 

 shock, and indirectly begets continuity of movement, a, angle formed by femur 

 with ilium; 6, angle formed by tibia and fibula with femur^ c, angle formed by 

 phalanges with cannon-bone; e, angle formed by humerus with scapula; /, angle 

 formea by radius and ulna with humerus (Pettigrew). 



there is also, in all cases perhaps, a united action ; the one 

 set, however, preponderating over the other, and usually sev- 

 eral muscles, whether of the same or different classes, act to- 

 gether. 



Standing itself requires the exercise of a large number of 



