POSTERIOR MEMBER. 



259 



elsewhere, the extensor muscles hinder this closing of the' angle by 

 acting in the manner of a lever of the second class, or that of force. 

 The canon, which is a portion of the arm of this lever, takes its point 

 of contact upon the soil by means of the foot, and receives the weight 

 of the body upon the astragaloid pulley, while the power, represented 

 by the gastrocnemius and the perforatus muscles, maintains the equi- 

 librium of this weight by strong traction upon the extremity of the 

 calcaneus. 



A fact here strikes the mind of whoever considers the nature 

 of this power, that it has to overcome at every moment a resist- 

 ance of more than 100 kilogrammes ! It 

 is its relative feebleness; it is the small 

 volume of the fleshy body of the gastroc- 

 nemius and the perforatus muscles, and 

 even of the perforans, which can also sus- 

 tain the tibio-tarsal angle ; it is the small 

 volume of these agents, compared with the 

 powerful muscles of the croup and the 

 thigh, which Professor Lemoigne justly 

 regards as a key to the rigidity of the 

 member, — a key without which all the 

 other extensors would be deprived of their 

 fulcrum or point of support.^ It seems 

 that there exists here an enormous contra- 

 diction between the means at the disposal 

 of the organism and the effects which it is 

 to produce. 



This inconsistency is only apparent, 

 and disappears as soon as we examine the 

 mode of proceeding by which the extension 

 of the hock is effected. By reason of the 

 connections which exist between the femur 

 and the calcaneus, through the interven- 

 tion of the cord ab (Fig. 78), the opening of the femoro-tibial angle 

 cannot take place without producing coincidently and in the same pro- 

 portion the opening of the tibio-tarsal angle. 



As the opening of the former may depend upon the straightening 

 of the femur or of the tibia, under the influence of their proper exten- 

 sors, ef, cd, it follows that all muscular traction exerted on the summit. 



Fig. 78. 



1 A. Lemoigne, Note communiqu6e. 



