306 MUSCULAR CONTRACTION. L.ECT. XVI. 



latter terminate by spherical enlargements, and the tendons 

 glide over these, in proceeding to attach themselves in- 

 feriorly to the bone to be put in motion. 



Lastly, let us remark, that on the relative position of the 

 points of support (fulcra or props,) and of the points of ap- 

 plication of the resistance (or weight,) and of the power 

 (or force) in the levers of the animal economy, depend the 

 well-known relations between the spaces traversed by the 

 power, and the resistance, and the absolute forces which 

 they represent. In general, the levers of the human body 

 are of the third kind, so that the arm of the lever of resist- 

 ance surpasses that of the power. The fore-arm offers us 

 an example of a lever of this kind ; indeed, its point of 

 support is at the elbow-joint, its resistance is the weight of 

 the arm, which we presume to be applied at its middle, and 

 its power is the flexor muscles, fixed at the extremity of the 

 bones of the fore-arm. We need only compare the relative 

 points of application, of the power, and of the resistance, 

 with the point of support, to obtain numbers expressing the 

 ratios of the movements of the power and of the resistance, 

 such as they are furnished by theory. The extremity of the 

 fore-arm traverses an arc much greater than that described 

 by the flexor muscles; the first accomplishes its movement 

 with a velocity of 974 millimetres in the second ; the other, 

 on the contrary, with a velocity of 81 centimetres. 



In cases where it is necessary to make an equilibrium to 

 a greater force, by means of a smaller one, the lever of the 

 second kind is employed ; we have an example of this in 

 man, when standing on one foot, which thus supports the 

 whole weight of the body. 



Borelli endeavoured to value the force of a great number 

 of muscles, and deduced, from the numbers found in his 

 experiments, the amount of force lost in most muscular 

 movements, in order to obtain velocity. We shall notice 



