242 VETERINARY PHYSIOLOGY 



The stride in the gallop is about ]5 to 20 feet. The 

 speed is variable. Race horses attain a speed of 30 to 35 

 miles an hour on a race course of one to two miles length. 



Canter. — The canter is a less energetic gallop. At one 

 moment all the feet are off the ground, and they are planted 

 in the same order as in the gallop — near hind, off hind, 

 near fore. But while in the gallop the near bind has left 

 the ground before the near fore is planted, in the canter all 

 these are on the ground at once, and it is only as the off 

 fore comes to the ground that the near hind followed by the 

 near fore is raised. The off hind and then the off fore next 

 follow, and all the feet off the ground. Both the length of 

 the stride and the speed are less in the canter than in the 

 gallop. 



Jump. — The fore legs propel the body upwards, and the 

 hind legs give a further forward and upward propulsion, and 

 are then fully flexed under the body to clear the obstacle. 

 The animal alights on its fore feet, one reaching the ground 

 before the other. 



6. Work of Muscle. 



As the result of the changes in shape, muscle performs 

 its orreat function of doincf mechanical work ; and the most 

 important question which has to be considered in regard to 

 muscle, as in regard to other machines, is the amount of 

 work it .can do. The work unit generally employed is the 

 kilogram-metre — the work required to raise one kilogram to 

 the height of one metre against the force of gravity. 



Since the work done depends upon the weight moved 

 and the distance through which it is moved, the work-doing 

 power of muscle is governed by the (a) force of contraction, 

 i.e. the tension developed which determines the weight 

 which can be lifted, and by (b) the amount to which the 

 m^uscle can shorten, for this governs the distance through 

 which the weight may be moved. 



It has been already shown that the force of contraction 

 depends upon the sectional area of a muscle. A. thick 

 muscle is stronger than a thinner one. On the other hand, 

 the extent of contraction depends upon the length of the 



