SPLINTS. 



231 



purposes, the third digit of all four legs became more useful, 

 with the result of increase in its size, and of diminution in the 

 volume of its fellows. 



An examination of our own liand, shows muscles which are 

 placed between our metacarpal bones (the bones between tlie 

 wrist and fingers); consequently we are able to slightly alter the 

 width of tlie palm of the hand, and separate our fingers one from 

 the other, or draw them together. The piossible amount of separa- 

 tion of the metacarpal bones and their respective fingers varies in 



Fig- 77- — Splint on outside of 

 off fore, 



proportion to the distance from the wrist. There is a somewhat 

 similar condition in tlie metacarpal interosseous muscles of the 

 dog. Decrease of this lateral play (or fanning-out action with 

 the wrist as a pivot) of the metacarpal bones, is accompanied by 

 diminution of the distance at which these bones are apart. This 

 curtailment of space has reached its maximum extent in the case 

 of the ox's third and fourth metacarpal bones, which are fused 

 into the one bone that forms liis cannon bone ; and a similar 

 condition exists in his hind legs, namely, in his metatarsal bones. 

 At first glance, the cannon bone of the ox might appear to be a 

 single bone, but it consists of two bones (third and fourth 



