THE STIFLE. 263 



THE STIFLE. 



The upper bone of the thigh is united to the lower by a' somewhat com- 

 pHcated joint. It terminates by two round prominences behind, which 

 are received into slight depressions on the upper surface of the lower bone; 

 and in "front is a curious groove over which plays a small irregular bone, 

 the patella or stifle bone. The whole is called by farriers the stifle joint. 

 The patella (Q, p. 63) answers to the kneepan in the human subject. Some 

 of the tendons of the strongest muscles of the upper bone of the thigh are 

 inserted into it, and continued from it over the lower bone. This important 

 joint is hereby much strengthened ; for the proper ligaments between the 

 upper and lower bones, and these additional tendons and ligaments from the 

 patella, must form altogether a very powerful union. The patella likewise 

 answers another and even more important purpose. The tendons of some 

 strong muscles are inserted into it. When these muscles are not in action, 

 the patella lies in the groove which nature has contrived for it ; but when 

 they begin to contract, it starts from its partial hiding-place, becomes pro- 

 minent from the joint, and alters the line of direction in which the muscles 

 act : it increases the angle, and thus very materially increases the power 

 of the muscles. 



The lower bone of the thigh is double : the larger portion, in front, 

 extending from the stifle to the hock, is called the tibia. The smaller bone, 

 or fibula, behind, see R, p. 63, reaches not more than a third of the way down. 

 It is united to the shank bone, Uke the splint bone, by a cartilaginous sub- 

 stance, which soon is changed for bone. Of the use of these little bones 

 we cannot speak 



The lower bone of the thigh forms an angle with the upper, the reverse 

 of that which exists between the upper bone and the pelvis. The object 

 of this is twofold, — to obviate concussion, and to give a direction toj the 

 muscles favourable to their powerful action ; and in proportion to the 

 acuteness of the angle, or the degree in which the stifle is brought under 

 the horse, will these purposes be accomplished. There is a great deal of 

 difference in this in different horses, and the construction of this part of 

 the frame is a matter worthy of more regard than is generaUy paid to it. 



This part of the thigh should likewise be long. In proportion to the 

 length of the muscle is the degree of contraction of which it is capable ; 

 and in proportion to the contraction of the muscle is the extent of motion 

 in the limb : but it is still more necessary that this part of the thigh should 

 have plenty of muscle, that strength may be added to this extent or compass 

 of motion. We should not expect much endurance from a horse with a thin 

 arm : a horse with thin and lanky thighs cannot possibly be good for anything. 

 In our cuts, p. 259 and 260, the principal muscles of this part'of the thigh 

 are delineated. They are usually somewhat prominent, and may readily 

 be traced in the living animal : a very brief notice of them may not be 

 uninteresting. 



We will first take the external ones, beginning in front. The continua- 

 tion from g, p. 260, is the tendinous expansion given to bind and strengthen 

 these muscles. 



71 is a very important muscle : it is the principal extensor muscle of the 

 hind-leg {extensor pedis, extensor of the foot). It arises from the lower 

 part of the upper bone of the thigh, and from the upper part of the lower 

 bone. It is a strong, round, fleshy muscle : a little before it reaches the 

 hock it will be seen to assume a tendinous form. It is covered and 

 defended by a sheath of its own j ^nd the cut will show the bands by which 



