LOCOMOTOR SYSTEM 60 1 



The Reciprocating Action of Stifle and Hock. — From what has 

 been said, it is evident that flexion and extension of stifle and 

 hock are identical in their action. When the stifle is extended, 

 the hock is automatically extended, nor can it under any circum- 

 stances flex without the previous flexion of the stifle. There is 

 no parallel to this in the body. The two joints, though far 

 apart, act as one, and they are locked by the drawing up of the 

 patella, and in no other way (Fig. 191, 1). The so-called disloca- 

 tion of the stifle in the horse is a misnomer. That the patella is 

 capable of being dislocated is beyond doubt, but the ordinary 

 condition described under that term, when the stifle and hock 

 are rigid while the foot is turned back with its wall on the ground, 

 is nothing more than spasm of the muscles which keep the patella 

 drawn up (Fig. 191, / /). The moment they relax the previously 

 immovable limb and useless foot have their function restored as 

 if by magic, but are immediately thrown out of gear in the course 

 of a few minutes as a recurrence of the tetanus of the patellar 

 muscles takes place. The fascia of the thigh, like that of the 

 arm, is a most potent factor in giving assistance to the constant 

 strain imposed on the muscles of the limbs during standing. 



Below the hock the hind-limb is arranged like that of the fore, 

 the deep flexor (perforans) receiving its additional support from 

 the ' check ligament,' as in the fore-leg (Fig. 191, 6). 



The natural attitude of standing adopted by the horse is to rest 

 on three legs — one hind and both fore. If he is alert, he stands 

 on all four limbs ; but if standing in the ordinary manner, he 

 always rests one hind-leg. He does not remain long in this 

 position without changing to the other. Hour by hour he 

 stands, shifting his weight at intervals from one to the other 

 hind-leg, and resting its fellow by flexing the hock and standing 

 on the toe. He never spares his fore-limbs in this manner in a 

 state of health, but always stands squarely on them. The 

 moment he places one fore-foot in advance of its fellow — ' point- 

 ing,' as it is termed — the experienced eye knows that something 

 is wrong. Many years ago the writer suggested that the periodical 

 resting of the hind-feet was the possible explanation of their 

 freedom from navicular disease. The horse only rests the fore- 

 feet when they are already subjects of this disorder. 



Distribution of the Weight on the Limbs. — The fact that the 

 animal rests the hind-limbs, and never the fore, suggests that 

 the weight carried by the former is greater than that carried by 

 the latter. The reverse, however, is the case. The fore-legs 

 carry from 9 to 19 per cent, more weight than the hind. The 

 weight on the fore-limbs is increased when the head is depressed, 

 and reduced when it is raised. The latter movement displaces 

 the centre of gravity backwards, and throws more weight on the 



