The metatarsus becomes more nearly horizontal, and 

 the tibio-metatarsal angle closes at the end. 



The muscles which put these different levers into mo- 

 tion are the " fascia lata " (the flexor of the femur, which 

 goes from the ilium to the stifle), the "triceps crural," 

 the tibial extensor situated on the forward face of the 

 femur, and finally the flexor of the metatarsus (situated 

 on the lower part of the femur and the forward part of 

 the tibia). 



These muscles have to overcome only the resistance 

 represented by the weight of the portion of the leg which 

 they have to move; they therefore do not need much 

 strength and could get along with fairly short lever arms. 

 But there is an advantage in having the widest possible 

 oscillation, so that the hind foot may resume contact with 

 the ground as far under the mass as possible. To this 

 end the thigh must flex as much as possible, therefore the 

 " femoral flexor " must be as long as possible. It is also 

 necessary that the leg should become as upright as pos- 

 sible, and to that end the tibial-extensor must be as long 

 as possible. This double condition can be obtained only 

 with great length of femur. Besides, great length of this 

 lever becomes very advantageous when the horse is gal- 

 loping on heavy ground, for it is the femoral-flexor 

 whose duty it is to overcome the resistance of the earth 

 and pull the feet out of the mud. 



It is easy to see from the sketch (Fig. 8) that a change 

 in the skeleton by which the femur is lengthened rela- 

 tively to the tibia, brings the hind foot further forward 

 under the mass, and later to the ground. 



This is easily seen by examination of the leg A B C D 

 and of the leg (with the lengthened femur and short- 

 ened tibia) A B' C D'. 



This same sketch shows that the opposite result would 

 be produced if the tibia were lengthened at the expense 



45 



