172 THE STRUCTURE OF THE HOESE. 



are almost all either simple " flexors/' bending the 

 distal segments backwards on the segment above, or 

 " extensors/ 7 returning them to the straight position. 

 The structure of the joints prevents the segments be- 

 ing bent forwards much beyond a straight line with 

 the segment above. The extensors are placed upon 

 the anterior or dorsal, and the flexors on the pos- 

 terior or ventral surface of the limb. 



In the human arm and hand there are muscles 

 having many other functions, such as turning the 

 hand round, spreading the fingers and bringing them 

 in contact again, which, of course, are not required 

 in the horse. In the limbs of all mammals having 

 the typical number of five digits completely de- 

 veloped, the muscles, as might be supposed, are as 

 numerous and arranged on much the same general 

 plan as in man. It is, however, very remarkable 

 that in the horse's limbs many more muscles exist 

 than would be thought necessary for the very simple 

 actions they have to perform. But it appears that 

 the reduction of bones to a rudimentary condition, 

 as in the case of the ulna and the fibula, or their en- 

 tire loss, as in the case of four of the toes, has taken 

 place more thoroughly than, and in advance of, that 

 of the muscles which were originally connected with 

 these bones, many of which linger, as it were, behind, 

 though with new relations and uses, sometimes in 



