GREGORY, QUADRUPEDAL LOCOMOTION 



275 



off the ground at once in seven out of nine phases of one stride. The 

 same figures show that the elephant has three feet on the ground together 

 during five-sixths of one stride, and during the remaining sixth the body 

 is supported by one fore foot and the opposite hind foot, whereas the 

 horse in question never has three feet on the ground together during the 

 stride there pictured. Thus it will be seen that the "acceleration mere- 



E 



Fig. 1. — Graviportal and cursorial modes of locomotion contrasted in the anible of the 

 elephant (I) and gallop of the horse (II) 



I after Muybridge ; II after Stillman 



ment" of the stride and the ballistic power of the limbs are at a maximum 

 in cursorial animals and at a minimum in graviportal animals. The 

 "acceleration increment" will no doubt increase also with the potency of 

 the psychic motive and of the neural stimulus (cf., p. 282). 



In brief, the factors of length of stride are (1) length of limb, (2) 

 angle of stride, (3) acceleration increment. 



