64 PEOCEEDINGS OF THE ACADEMY OF [1887. 



fore limbs the labor of accommodating themselves to the rate of work 

 of their more powerful associates. When an animal is moving at a 

 high rate of speed, as in the gallop, the synchiral action of the hind 

 limbs projects the body with such force as to compel the fore limbs to 

 act simply as props which successively carry the body forwards until 

 one of the hind limbs is again in position to give the body a second 

 impetus. In proof of this assertion it is only necessary to observe 

 that the greatest height attained by the trunk is that secured by the 

 rump when both hind feet are off the ground. The statement gener- 

 ally made that the horse leaves the ground by one of the fore feet 

 creates the impression that he gains the springing force from this 

 foot, all the previous movements being in preparation for such a 

 .spring. In place of this statement another is here substituted, viz., 

 that the horse springs from that hind foot which last leaves the 

 ground and is " off" from all feet when he simply relinquishes the 

 support afforded by the last prop, that is to say the last fore foot. 



If the fore and hind limbs were based on the same plan the motion 

 of an animal would be either a series of springs the two feet push- 

 ing against the ground at the same moment or a series of steps, the 

 two feet moving alternately. While closely resembling one another 

 the two limbs are not on the same plan. If any motion takes 

 place in the vertebral column at the time that the fore limb is 

 moving it is noticed that it occurs in the region of the neck. The 

 scapula has a slight motion downward and backward. The motion 

 in the hind limbs occur in the region of the lumbar vertebrse while 

 the pelvic bones are fixed. The limit of the forward motion of the 

 hind limbs is dependent upon the flexibility of the lumbar vertebrae. 

 The limit of the similar motion of the fore limb is determined by 

 the action of the muscles alone. The forward motion of the fore 

 limbs is essentially the same in all animals ; ])ut the forward 

 movement of the hind limbs is variable, because the lumbar vertebrae 

 differ in degrees of flexibility. In unguiculates there is more lumbar 

 flexibility than in ungulates. In backward movements the opposite 

 obtains, for in these positions the fore limbs can be carried back 

 to a variable distance. In the deer and its congeners the fore foot can 

 be brought to a point near the centre of the body, and the limb be 

 vertical. In the horse the fore limb in backward strain is very 

 oblique and the foot w'hile well placed under the trunk cannot reach 

 the centre. In the macaque the fore foot cannot pass beyond a 

 vertical line which intersects the trunk a little back of the shoulder- 

 joint. The l)ackward movement of the hind limb is nearly the 



