744 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the foot to the ground, the axis of the limb being now directed obliquely 

 downward and forward. The body weight is then shifted to this limb 

 through the action of the adductors, the limb again passing into a more 

 or less marked position of flexion. The croup muscles then contracting, 

 the pelvis is advanced, assisted by the extensors of the femur, which find 

 a fixed point in the knee, while at the same time the gastrocnemius 

 muscle, contracting, opens the angle of the hock-joint and elevates the 

 pelvis from the increase in the length of the axis of the limb. Through 

 these motions the line of the hind leg gradually becomes vertical, passes 

 the perpendicular, and is then directed downward and backward from 

 the advance communicated to the body (Pig. 306). When the highest 



D 



Fig. 306.— Oscillation of the Extended Hind Leg. {Colin.) 



The foot being on the ground at D, the hip-joint describes an arc of a circle, ABC, the lines A D, 

 B D, and C D representing the changing axis of the hind leg. 



degree of extension is reached the weight is shifted to the opposite limb, 

 and after complete flexion the pendulum motion is repeated. 



In these motions the hind leg does not move in the plane of the line 

 of direction ; in rapid movement the knee and tip of the foot are some- 

 what everted through the action of the iliacus muscle until the foot 

 strikes the ground. In slow motions, on the other hand, especially when 

 bearing heavy weights, the knee is directed inward from the action of 

 the adductors and tension of the femoral fascia, while the hock is everted, 

 thus turning the toe toward the median line. 



(a) The Walk. — In walking the body is supported by two legs while 

 the other two are describing the pendulum motion, the support being 

 alternately on diagonal feet and then on the two feet of the same side ; 



