736 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



constantly tends to become exaggerated by the weight which the upper 

 extremity supports, it never passes certain limits on account of the pres- 

 ence of the spiral ligament of the pastern-joint. Without this ligamentous 

 support muscular action would be insufficient to prevent extreme flexion, 

 but by means of the ligament, which in the horse and ruminant is composed 

 of powerful non-elastic tendinous fibres, represented in the carnivora by 

 muscular fibre, the support of the body is rendered possible without 

 fatigue. 



In the case of the posterior limbs great deviation from the vertical 

 is met with, and that their obliquity should be restrained within certain 

 limits considerable muscular effort is required and the mechanical dispo- 

 sitions of the power is more complex (Fig. 298) than in the case of the 

 thoracic members. In the hind leg four angles are met with, viz. : in 

 the hip-joint, the knee-joint, the hock-joint, and the pastern-joint, the 

 degree of these angles being governed by the angle which the axis of the 

 femur makes with the vertebrae and the position in which the hind foot 

 is placed. In the resting position of the hind extremity the line of direc- 

 tion of the body weight passes from the centre of the hip-joint vertically 

 downward to the centre of the hock-joint, and then, deviating about 10 

 from the direction of the metatarsus, passes behind the pastern-joint 

 to the ground. The pelvis is very oblique relatively to the trunk in the 

 horse, ox, and most ruminants and carnivora. The femur is obliquely 

 connected with the pelvis, downward motion of the pelvis and backward 

 motion of the femur from the body weight being prevented by the 

 abdominal recti muscles, whose tendons, being inserted in the pelvis, by 

 their tension tend to draw the hip-joint anteriorly. The gluteal muscles, 

 arising from the ilium and passing over the hip-joint to the femur, act 

 in the same direction, not only preventing forcing backward of the hip- 

 joint, but in its contraction pressing the hip-joint forward. The leg is, 

 like the femur, flexed, its obliquity being limited by the tension of the 

 tendons of the extensor muscles, which pass over the anterior surface of 

 the knee-joint, by the ligaments of the knee-joint, and by the tibio-tarsal 

 muscle, which in the solipedes throughout its entire length consists of a 

 strong aponeurotic band, thus being analogous in its action to the coraco- 

 radial muscle of the anterior extremity. The flexion of the metatarsus 

 on the leg is limited especially by the gastrocnemius muscles and: by the 

 superficial flexor of the phalanges, which in the suspensory ligament 

 becomes reduced to a cylindrical cord and flattened out at its passage 

 over the summit of the calcaneum. The inclination of the phalanges on 

 the metatarsus is prevented by a ligamentous suspensory apparatus 

 similar to that of the anterior extremity. 



From the above it is seen that the extremities in standing support 

 the body only by muscular effort, principally that of the extensors. 



