304 MUSCULAR CONTRACTION. LECT. XVI. 



long since, that the weights, which cylindrical or prismatic 

 rods can sustain without yielding, are in the inverse ratio 

 to the square roots of their length, provided that their na- 

 ture and section remain constant. If we express by 1, 2, 

 3, 4, &c., the lengths of the homogeneous rods, the weights 

 that they can support without bending are expressed by the 

 numbers 1, , , T J F , &c. Hence, the bones must have dif- 

 ferent lengths, according to the different efforts which they 

 are required to sustain. 



Salidee demonstrated longsiaee, that within certain limits 

 of thickness of the osseous wall, the resistance which bones 

 oppose to fracture, against a force applied laterally, is 

 greater in a hollow cylinder of large diameter than in a 

 solid cylinder, and consequently one of smaller diameter. 

 All bones are constructed so as to give the necessary resist- 

 ance, without greatly increasing the weight. 



Muscular Force. Let us, ia the last place, speak of 

 muscular power, a subject, which I must admit is not more 

 advanced now tban, it was a century ago, when Borelli 

 begaa to study k. In general, we observe that, in the 

 employment of muscles in locomotion, their arrangement is 

 so combined as to give the greatest possible velocity and 

 extent of motion.,, without sacrificing the simplicity, harmony, 

 and elegance of the aifferent parts of the human machine. 

 In every possible case, the following conditions are united 

 to realize these results : 



1st. The oblique insertion of the muscular fibres in the 

 tendon. 



2d. The obliquity of the direction of the tendon to the 

 axis to which it is attached, and on which it must act. 



3d. The proximity of the points of insertion of the 

 tendons to the articulation of the bones, which serve as 

 points of support. 



The priaciples established by Borelli for calculating the 



