360 NAVIX ox THE HORSE. 



by two deep grooves, a central ridge between tliem, and 

 another at each side. It rests on the astragalus, which has 

 two elevations exactly corresponding with the grooves in the 

 lower head of the tibia. At the back, its rounded surface ex- 

 actly fits into a concavity of the os calcis, or heel-bone, to which 

 it is firmly bound by ligaments. 



The fbula is placed at the back of the tibia, and extends 

 about one-third of the way down it. The two bones are united 

 by cartilage in early life, but this soon becomes changed into 

 bone. The lower bones of the thigh stand in an oblique, or 

 slanting, direction backward, thus forming an angle with the 

 femur. Two objects are thus accomplished— concussion is pre- 

 vented, and the muscles are enabled to act wdth much greater 

 power. And in proportion to the acuteness or sharpness of the 

 angle thus formed, known by the knee, or stifle-joint, standing 

 well under, will these objects be accomplished. There is great 

 difference in this respect in different horses. This is a point 

 worthy particular attention. The tibia should be long and 

 supplied with full, strong muscles. It has been already ob- 

 served how important this is in the arm, and it is, if possible, 

 more necessary here. 



The astragalus is a thick, heavy bone, situated beneath the 

 lower head of the tibia. It is the form of a half-circle from 

 above forward, and marked by a deep groove, with a high pro- 

 jection on each side, which fit into grooves in the lower head 

 of the tibia. By this arrangement this joint admits of a very 

 extensive forward motion. Behind, it is firmly attached to the 

 OS calcis, or heel-bone, which forms the backward projection of 

 the hough. Below, it rests on the larger of the thre<3 wedge- 

 bones. 



The OS calcis (sjmr-bone) is a flat, thick bone, situated at the 

 back part of the hough, and looking backward and upward. 

 It projects back a considerable distance. Some of the most 

 powerful muscles are inserted into its extremity by what is 

 generally called the hamstring. It is united by articulation 



