148 THE SURGICAL ANATOMY OF THE HORSE 



the limb from the tarsus downwards. The bar of the lever is, however, 

 the same in both cases. Since the bar is made up of a number of 

 separate osseous segments, it will be evident from the principles of 

 leverage, that these must be united to one another in such manner as to 

 give the bar that degree of rigidity which will permit of the transmission 

 of the action of the power to the weight, and which will also resist the 

 breaking action of the fulcrum. During the action of the gastrocnemius 

 muscle, rigidity and resistance to the action of the fulcrum are afforded 

 by the calcaneo-metatarsal hgament, so that this ligament plays a very 

 important part in flexion and extension of the true hock joint. 



Sprain or injury to the calcaneo-metatarsal ligament gives rise to the 

 well-known and by no means uncommon surgical affection of " curb. 



Commonly the term curb is applied to any enlargement which is 

 placed on the postero-inferior aspect of the joint, and there has in the 

 past been considerable divergence of opinion as to the particular structure 

 which is thickened. Percival maintained that it was a thickening of 

 the deep fascia. Others attributed the enlargement to a thickening 

 of one or other of the flexor tendons in this situation. There can be 

 little doubt that the structure upon which greatest strain is thrown, and 

 which is most likely to be damaged at this particular seat, is the calcaneo- 

 metatarsal ligament. 



From what we have already said it will be gathered without diiEculty 

 that there are certain kinds of hocks which will be more predisposed to 

 the formation of curbs than others. Thus, for instance, in hocks in 

 which the bar of the lever is not straight but is naturally a little bent, 

 with its convex surface directed backwards, there will obviously be 

 much greater strain thrown upon the ligament in maintaining the 

 necessary rigidity. Such are commonly known as " sickle hocks," 

 and in these the bar is bent near the point of action of the fulcrum. 

 Since, also, the force at which the power acts is in direct proportion to 

 the distance of the fulcrum from the point of application of the power, 

 the action of the gastrocnemius is most powerful in extending the hock 



