162 THE STRUCTURE OF THE HORSE. 



is, in fact, so short, and placed so nearly horizontally, 

 and so covered up with muscles, that externally this 

 segment makes no distinct appearance, being buried in 

 the body or trunk, from which the limb only separates 

 itself at the commencement of the second segment 

 or elbow-joint, instead of at the shoulder, as in man. 

 The skeleton of the second segment or forearm in 

 man consists of two bones placed side by side (1) 

 the ulna, which is connected with the huinerus by a 

 simple hinge- joint, allowing motion of bending (flex- 

 ion) and straightening (extension) only in one plane, 

 and (2) the radius, which turns or rotates in a pecul- 

 iar way round the former, carrying the hand with it, 

 and thus enabling the palm or the back of the hand 

 to be turned uppermost at will motions described as 

 " supination " and " pronation." In the horse there 

 is nothing of the kind ; the radius is a strong bone 

 of almost equal size at both ends, and the ulna is 

 reduced to its upper part, which is firmly fixed to the 

 radius, its only function being to strengthen the very 

 perfect hinge of the elbow-joint behind. The hand 

 is thus permanently fixed in the prone position, with 

 its dorsal surface turned forwards. A flexible and 

 revolving wrist- joint, though essential to the perform- 

 ance of the duties required from the human hand, 

 would be quite incompatible with those needed from 

 the corresponding part of the horse. 



