150 COPE. [Vo. III. 
impact and longitudinal strain. These two forms of energy 
move in directions opposite to each other; the one as compres- 
sion in the direction of the length of the bone; the other, as a 
stretching in the direction of the length of the 
bone. Both processes alike appear to have stim- 
ulated growth in the direction of the length of 
the bone. 
Figure 1.— A. Phenacodus primevus, fore and hind limbs; &. Homo sapiens, 
fore and hind limbs. 
