424 MOVEMENTS OF THE LIMBS 



the OS calcis by the gastrocnemius. A foot with a long load-arm, 

 i.e. with the load near the power, is designed for speed not power — 

 well adapted for running. On the other hand, the further the 

 load is from the point of application of power, in this case, the 

 longer the heel, the smaller will be the force necessary to lift 

 the body. That this is so, may be inferred from a study of the 

 development of the gastrocnemius muscle compared with the 

 length of the heel bone. Europeans have short heel-bones and 

 well-developed, bulky calves, while Africans have long heels and 

 ill-developed calf muscles. 



Class III. The point of application of the power is between 

 fulcrum and load. This power must always be greater than the 

 load. It is the commonest class of lever in the body, and this is 

 to be expected, as its use results in the most rapid action possible. 

 Speed is obtained, as before, by shortening the power-arm. In 

 the arm, the Brachialis muscle is inserted about 1 cm. beyond 

 the fulcrum (ell)ow), while the total length of the load-arm (fore- 

 arm) is about 30 cm. The result of this arrangement is that the 

 load (hand) moves with about 30 times the speed of the bone 

 at the point of the application of the power. " Speed is gained 

 at the expense of power." It follows that while a long-armed 

 man may be able to give a quick blow he will be quite unable, 

 unless his brachial muscles are abnormally developed, to give a 

 heavy one. 



This introduces a point to which the author of the " Tarzan " 

 stories paid little attention. Tarzan was able to hold his own 

 among the tree tops. Now, man has a fore-arm considerably 

 shorter than the upper arm while the anthropoid ape has a fore- 

 arm only a little short of twice as long as its humerus. This gives 

 it a long and quick reach. In swinging and climl)ing, the upper 

 arm is the lever employed to lift the body, mainly by the con- 

 traction of the Brachialis muscle ; and the origin of the Brachialis 

 over half-way up the humerus from the elbow (fulcrum) gives a 

 power-arm with rather more power than speed. That is, a short 

 humerus is a necessity for climbing animals — to furnish strength, 

 just as the long forearm is necessary to give agility. To have 

 equal climbing power, man would need to have extraordinarily 

 bulky Biceps, etc., and this would not aid him when he desired 

 to swing and seize distant branches surely and rapidly. 



So far, we have dealt with the levers of the body in a general 

 sense, as if they were straight bars. As a matter of fact, none of 

 the bones of the body can be considered as straight levers, and none 

 of the muscles act absolutely at right angles to the length of the 

 bone. The length of the effective power and load arms may be 



