Discussio:^- 195 



chiefly the obturators, pyriformis, gemelh, and to some extent 

 the quadratus femoris — which act as rotators of the femur 

 must be efficient. 



It will be noted that the distal extremity of the femur is 

 vastly different from that of the humerus. It must be 

 stronger, with a heavier articulation to withstand lateral 

 stress, and it must be of a decidedly different form to 

 accommodate the broad head of the tibia, rather than the 

 peculiarities of the radial and ulnar articulations. Partly 

 because of these facts and probably because of the differences 

 in function between the low^er leg and arm, there are not as 

 many muscles originating from the epicondyles of the femur 

 as from those of the humerus, more of them arising from the 

 heads of the tibia and fibula, and hence, presenting a simpler, 

 less specialized condition. 



Analogous to the relationship of the olecranon with the 

 ulna is that of the patella with the tibia, although the latter 

 is a separate bone. It is by means of the patella and its 

 ligament that the three vasti and three other direct flexors 

 of the lower leg operate. Due to their efficiency and the 

 normally flexed, static position of this segment, it now has 

 no indirect extensor operating as such. 



The static position of the lower leg or third segment is at 

 an angle of less than 90 degrees with the femur, and its 

 functional arc of motion while the animal is running in its 

 normal, crouching posture is therefore probably greater than 

 in man, although possible arc of motion in the latter is 

 evidently no smaller. The tibia can assume a position on a 

 line with the femur, but it is doubtful if this segment is 

 extended to the utmost during any part of the stride, al- 

 though it is conceivable that this may be the case at the 

 culmination of the rearward swing. Flexor muscles attached 

 to it as in man would be very inefficient and many of them 

 are therefore placed well down upon the lower leg. Not- 

 withstanding such attachment the shank may be fully 



