CURB. 



1015 



of the small external metatarsal bone, to thickening of the skin, 

 annular ligament, or perforatus tendon, or to distension of the tarsal 

 sheath of the perforans, which lies at the inner side of the posterior 

 border of the hock. These conditions, which are usually easy of 

 recognition, though sometimes erroneously described as curbs, must, 

 however, be distinguished from thickening of the calcaneo-metatarsal 

 ligament or true curb. The upper end of this ligament is attached 

 to the posterior border of the tuber calcis, whence it passes down- 

 wards to become inserted on the cuboid, and the head of the external 

 small metatarsal bone. In consequence of sprain, it often becomes 

 inflamed and thickened, or the inflammation 

 may possibly induce changes in the adjacent 

 joint. Distension of the tarsal sheath, or 

 thickening of the perforans tendon, is usually 

 easy to differentiate from curb, inasmuch as 

 the distension or tendinous swelling lies to the 

 inner side of the seat of curb and extends 

 further downwards on the leg. Strain of the 

 perforatus tendon at the upper extremity of 

 the shank may cause difficulty in accurate 

 diagnosis, for the tendon lies over the calcaneo- 

 metatarsal ligament, but the superficial position 

 of the thickening in perforatus strain should 

 enable a distinction to be made between it and 

 disease of the ligament or curb. 



Causes. The lower portion of the limb, from 

 the point of the os calcis to the ground, may 

 be regarded as a long lever. The pull of the 

 gastrocnemius muscle acting on the point of 

 the calcis tends to break this lever in two 

 across the fulcrum, represented by the lower 



end of the tibia. The tissue which resists the breaking strain 

 and holds the os calcis in line with the other bones of the limb is 

 the calcaneo-metatarsal ligament. It is easy, then, to estimate the 

 great strains to which this ligament is subject, and to understand 

 why it frequently becomes injured. Horses with " tied-in " and 

 " sickle-shaped " hocks are especially predisposed to curb, and, if 

 incautiously worked before maturity, generally develop it. The 

 reason appears to be that, as the ligament serves to unite the meta- 

 tarsus to the os calcis, and as the calcis acts like a lever, to the end 

 of which are attached the extensor tendons, especially the tendon 

 of the gastrocnemius, the more nearly the bend of the hock approaches 



Fig. 544.— Curb. 



