606 A MANUAL OF VETERINARY PHYSIOLOGY 



in the sweep it makes on flexion of the elbow. It is greatly 

 exaggerated in some horses. 



The Knee-joint consists of three main joints and numerous 

 minor ones. The articulatory surface of the radius with the 

 upper row of knee-bones has no parallel in the body ; it is a surface 

 both deeply concave and markedly convexo-concave. The con- 

 cavity and convexity on the radius form condyles of which the 

 inner is more curved than the outer. The concavity on the 

 anterior part of the radiocarpal articulation rests on the convex 

 surface of the upper row of knee-bones, and in this way a firmer 

 and closer union between these surfaces is obtained, such as is 

 needed in the upright condition of the limb. But when this 

 joint is flexed, the convex posterior surface of the radius comes 

 forward ; this depresses the scaphoid (radiocarpal) , and produces 

 between it and the semilunar (intermediate carpal) a very im- 

 portant movement by which the foot is thrown slightly out- 

 wards, probably with the object of enabling it to clear the 

 opposite limb. The upper joint of the knee possesses the largest 

 range of motion, the middle joint very much less, the lower joint 

 hardly doing more than gliding on its fellow. Percivall pointed 

 out many years ago that the trapezoid rests wholly on the head 

 of the inner splint bone, which explains the frequency with 

 which this bone becomes affected with ' splint. ' 



The Fetlock-Joint forms a special variety of articulation, 

 one which is firm and rigid anteriorly, elastic and yielding 

 posteriorly. This is effected by introducing two sesamoid bones 

 into the fetlock articulation, and suspending them between 

 ligaments : the structure by means of which the sesamoids are 

 suspended is the Suspensory Ligament (Fig. 186). This runs 

 from the back of the large metacarpal bone to the fetlock, 

 receiving insertion into the sesamoids. The latter are floating 

 bones, and, speaking more generally, perhaps, than an anatomist 

 would admit, they are embedded in ligamentous material which 

 keeps them in their place. The suspensory ligament supports 

 them above and laterally ; the sesamoidal ligaments keep 

 them fixed below. The anterior face of these bones forms the 

 posterior face of the fetlock-joint. 



There is no other joint in the body the mechanism of which has 

 received so much attention as that of the fetlock and suspensory 

 ligament. The rival theories have been divided on the question 

 of the elasticity of the suspensory ligament. Gamgee (senior) 

 regarded it as absolutely non-elastic ; he did not believe that it 

 supported the sesamoids, but regarded it as acting powerfully 

 in flexing the foot, being brought into action or set free according 

 to the position of the limb. It was he who destroyed the notion 

 once and for all that the sesamoids moved up and down. 



