CAUSES OF UNSOUNDNESS. 115 



to, the sale. Cramp of the muscles of the stifle 

 brings about a similar class of signs, and it is very 

 easily confused with slipped stifle. 



The Hock. 



Introduction. — It is necessary that the reader of 

 a work of this class should acquire an elementary 

 knowledge regarding the anatomical conformation 

 of the hock, which includes the area lying between 

 the lower end of the second thigh and the upper 

 end of the cannon bone. For convenience, we may 

 say that the joint has a front face; and inner, 

 outer, and posterior surfaces. The extreme 

 posterior part of the hock corresponds to the heel 

 in man, and its summit is known as the point of 

 the hock, being formed by a single bone known as 

 the OS calcis. There is a large screw-like bone 

 that works in corresponding grooves on the lower 

 end of the second thigh ; this screw-like bone is 

 termed the astragalus, and its lower face articulates 

 with the smaller bones of the hock, with the os 

 calcis behind, and also with two other small bones 

 of the hock. The internal surface of the astragalus 

 is very rough and bears a small tubercle below. 

 The external surface is also rough, and has a 

 circular depression for the insertion of ligaments. 



8* 



