LOCOMOTOR SYSTEM 593 



by which means additional support under continuous strain is 

 obtained. But it is by the two long flexors, the superficial and deep 

 digital (flexor perforatus and per for arts) (Figs. 185, 5, 6 ; and 186) , that 

 the main support to the bony column is given, and this is obtained 

 through the limb bending forward at the fetlock and these two 

 tendons passing beneath and supporting the bent joint. The 

 weight of the body presses the fetlock to the ground. The 

 counteracting force of the flexor tendons sustains that weight, 

 and maintains the fetlock in position. They are not the only 

 mechanism supporting the fetlock, for there is the suspensory 

 ligament, of which later ; but the flexors are the chief support 

 and, if divided, the fetlock sinks appreciably closer to the ground. 

 The changes occurring in the fetlock-joint when an animal from 

 injury or other cause is compelled for some time to support its 

 body weight entirely on one limb throw light on the mechanism 

 of the joint. It is not the muscular portion of the supporting 

 flexors which gives way under the strain, but the tendinous portion, 

 and this is well seen at the fetlock- joint. The bursa of the 

 tendons at the part is dry ; the tendons are dry, yellow, and 

 shrunk. The interior of the fetlock- joint reveals nutritive 

 changes, brought about by long-continued compression. The 

 articular cartilage has become so thin that the bone has the barest 

 possible covering, the joint is dry and yellow, and so intense has 

 been the pressure that the actual pattern of one joint surface may 

 be imprinted deeply on its fellow, and this imprint is made on 

 the posterior part of the articulation, and not on the anterior ; 

 in other words, the pressure falls behind. 



The two long flexors running from elbow to foot are assisted 

 in their duty as weight-bearers by means of so-called check 

 ligaments (Figs. 185, 7, 8; 186). These ligaments are running, 

 not from bone to bone, but from bone to tendon, and make a 

 tendon function as a ligament by cutting off, as it were, the 

 muscular attachment beyond. The perforatus above the knee 

 and the perforans below it both receive a check ligament, which 

 under the long-continued strain of support enables the flexor 

 muscles to relax and obtain a much-needed rest. 



The mechanisms below the fetlocks are a continuation of those 

 above it, the same extensor and flexor tendons being employed 

 from elbow- joint to foot. The slope of the pastern is main- 

 tained by the flexors of the leg, and though a joint exists between 

 the second and third phalangeal bone, its function, when the 

 limb is in the standing attitude, is not in evidence. In looking 

 at the slope of the pastern, the eye always regards it as one bone, 

 instead of two. The reason is obvious. There is very little move- 

 ment in the joint between the corona and suffraginis at any time, 

 .and there is still less when standing. They are united by a dense 



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