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 sUpped 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* 



