LOCOMOTOR SYSTEM 615 



may frequently give way in its fellow through the latter supporting 

 extra weight, so that, quite apart from work, the legs may suffer in 

 their effort to support the weight of the body. During work the 

 strain on the limbs is of two kinds — i.e., that which arises when the 

 body is propelled from the ground, and that which occurs when 

 the body comes to the ground. One may be spoken of as the strain 

 of propulsion, the other the strain of impact. Of the two, the strain 

 of propulsion is the greater, and in consequence the limbs which 

 propel the body during the fast paces suffer from injury to a far 

 greater extent than those which receive it. Strain and concussion 

 in the limbs are provided against in several ways. The bony columns 

 of the legs, it will be observed, are broken up, the smallest segments 

 being nearest the ground, the largest away from it. The bones 

 forming the column are frequently arranged at an angle, by means 

 of which direct jar is minimised. This is especially the case in 

 the hind-limbs, which receive the weight of the body in all fast paces. 

 Joints of a non-rigid kind are formed in three parts of the limb, all 

 being close together and but a few inches from the ground. One 

 exists within the foot, another at the fetlock, and an imperfect one 

 at the pastern. These offer an elastic rather than a rigid resistance. 

 The muscles, tendons, and ligaments also play their part. Muscles, 

 we have seen, are perfectly elastic : it is a property which belongs to 

 them ; neither tendons nor ligaments are regarded as elastic, though 

 more than once attention has been drawn to the fact that there must 

 be some give and take in these tissues, some stretching and recovery. 

 That neither is capable of severe extension is undoubted, and nor- 

 mally, so long as the muscles maintain their complete command of 

 the limb, both tendons and ligaments are subordinate to them in the 

 matter of strain. When muscles tire and lose their elasticity, their 

 tendinous attachments suffer, and it is practically only at this time 

 that sprains of tendons occur. When a horse tires, it is the fore-leg 

 flexors which sprain, for the reason that the burden of propelling the 

 body falls on the flexor muscles of the fore-limbs ; the flexors of the 

 hind-limbs only receive the weight when the body comes to the 

 ground, and, relatively speaking, rarely suffer. 



The extensor tendons of the limbs never suffer, for the work done 

 by their muscles does not necessitate a powerful contraction such 

 as occurs with the flexors when they propel in the gallop 9 hundred- 

 weight (460 kilogrammes) of material a distance of several feet through 

 the air. This is why the flexor muscles tire in spite of their tendinous 

 intersections, and the moment this occurs the tendons have to take 

 the shock.* One can imagine that for some strides the check liga- 

 ments are useful accessories in helping the tendons to deal with 

 fatigued elongated muscles, but the attempt to propel the body from 

 the ground with tired muscles and a stretched tendon causes the 

 latter to yield, and one or both partly or completely give way, either 

 where the subcarpal check ligament joins, or between it and the 

 fetlock. The muscles never rupture, and the tendons rarely yield 

 at any other spot than between the fetlock and the middle of the 

 shank. Both tendons in this region are practically at their smallest. 

 Sprains of the flexor tendons do not occur at a walk, nor in the 

 stable from slipping, nor on the road from trotting ; they occur 



* We have seen (p. 588) that there is a great difference between the 

 post-mortem breaking-strain of the flexor as compared with the extensor 

 muscles of the fore-limb. 



