LOCOMOTOR SYSTEM 607 



The fetlock-joint furnishes the only example in the body of 

 a bone placed vertically resting on one placed obliquely. The 

 metacarpal rests on an inclined plane in the form of the suffraginis, 

 and but for the sesamoids would slip off at the back. It is one 

 of the functions of the sesamoids and suspensory ligament to 

 keep this bone in its place, and so support the fetlock under stress. 



The sesamoid bones are also intended to furnish the fetlock- 

 joint with a yielding articulation, which receives the weight of 

 the body when the foot comes in contact with the ground. At 

 the moment this occurs the whole pastern from fetlock to foot 

 becomes more oblique, giving the appearance of sinking, which 

 in reality occurs. The sinking, however, is not due to displace- 

 ment of the sesamoids, but to increased obliquity of the pastern 

 under stress, owing to which the suspensory ligament is under 

 great strain. It does not appear to be reasonable to deny it some 

 degree of elasticity — viz., the power to stretch slightly and then 

 return to its original length ; but the stretching is not great, and 

 can be reproduced on a limited scale by lifting up the opposite 

 fore-leg, and observing the tense, sharp lines produced in the 

 suspensory at the moment the fetlock descends, through increased 

 obliquity of the pastern. The evidence that the suspensory 

 supports the fetlock is shown by the effect of dividing it, which 

 brings the fetlock appreciably nearer to the ground, while the 

 evidence that the suspensory ligament only possesses limited 

 elasticity is furnished clinically by the frequency with which 

 it is sprained. If it were highly elastic, a sprain would be a 

 difficult matter. No one, for instance, ever heard of the only 

 elastic ligament in the body being sprained — i.e., the ligamentum 

 nucha — but a ligament of this nature in any part of the limbs 

 would be useless. If tendons and ligaments were highly elastic, 

 the efficient action of muscles would be destroyed, for during 

 contraction their tendons would be stretching instead of pulling. 



It is quite easy to show that in the ordinary standing attitude 

 the sesamoid bones, together with the posterior half of the 

 metacarpal articulation, bear the weight of the body, while 

 the anterior surface of the suffraginis and metacarpal takes 

 but a small share. The two movements of the fetlock-joint 

 are flexion and extension. Flexion in every other joint in 

 the body but the fetlock begins by bending, but when the fetlock 

 is flexed the pastern has first to become straight before it can 

 be bent backwards. Flexion of this joint is accomplished by 

 the perforans and perforatus, while extension is brought about 

 by the extensor of the foot and suffraginis. The more the foot 

 is extended, the greater the strain on the sesamoids, and the slip 

 of the suspensory ligament which joins the extensor tendon 

 (Fig. 186,) may at this time be associated with the action of this 



