5Q6 A MANUAL OF VETERINARY PHYSIOLOGY 



feltwork of ligamentous material, and, as we shall see later in 

 studying the limb in movement, the chief motion occurring in 

 the pastern bones is between the corona and pedis. 



The fore-limb is kept vertical and the pastern bent by the 

 insertion of the perforans tendon into the pedal bone ; every joint 

 from the elbow to the foot is locked by its extensor tendons and 

 supported by its flexors, the fascia of the arm binding up and 

 supporting both groups. 



In the hind-limbs the standing attitude is simpler, owing to 

 the existence of the hip- joints beneath the horizontal spine. 

 The attitude assumed by the legs is the result of flexion in some 

 joints, extension in others. The hip- joint is flexed by the psoas 

 magnus, iliacus, tensor fascice latce, gluteus super ficialis (gluteus 

 externus), and pectineus muscles. Considering the enormous 

 amount of muscular tissue belonging to the hind-quarters, it is 

 rather remarkable that so little of it is required for hip-flexion, 

 for the above, relatively speaking, are not bulky muscles. The 

 extensors of the hip- joint, on the other hand, are very large — i.e., 

 the insertions of the large biceps femoris, gluteus medius, and 

 semimembranosus (see Figs. 187 and 188). 



The above groups of muscles fix the head of the femur rigidly 

 so far as to-and-fro and outward movements are concerned, but 

 the joint has also to be supplied with support on its inner side, 

 and this is effected by the great and small adductors and gracilis. 

 The resultant of the pull of these muscles on the hip-joint is the 

 position assumed by the femur in standing, and the angle it 

 forms with the pelvis depends upon whether the limb is bearing 

 weight or resting. The joint below the hip is the stifle, and the 

 part this plays in attitude is considerable, for no flexion of the 

 hind-leg can possibly take place without the concurrence of the 

 stifle. The stifle is flexed by means of the biceps femoris, semi- 

 tendinosus, and gracilis (Figs. 187, 189) ; it is extended by the 

 rectus femoris and vasti muscles (Fig. 188). Unless these latter 

 concur, flexion of the stifle is impossible. So slight, indeed, is 

 the effort required to keep the stifle rigidly extended that if one 

 hand grasps the muscles inserted into the patella, and presses 

 the bone back on the femur — the horse having just been destroyed 

 — no ordinary force employed at the foot-end of the limb can 

 flex the hock, and the hock cannot flex without the stifle 

 flexing. 



Tendo-Ligaments of the Thigh. — From the above it is evident 

 that very little muscular effort is required to keep the largest joint 

 in the body fixed during the standing attitude. In addition to 

 the muscles inserted into the patella, the stifle is also kept 

 extended by the contraction of the anterior digital extensor 

 (extensor pedis), peroneus tertius, and tibialis anticus (flexor meta- 

 tarsi muscular and tendinous division) — a pair of muscles (Fig. 190) 



