THE SKELETON. 31 



bone, possessing great strength ; and we shall always find that 

 when strength is chiefly required, a cylinder is the favourite form. 

 In addition to this, in common with most of the bones of the 

 extremities, the middle is hollow, and contains the marrow, a 

 very light fatty substance, deposited in cancelli or bony cells. 

 The reason of this conformation is, that a certain bulk is neces- 

 sary for the attachment of muscles, and the utmost degree of 

 strength is required with the least quantity of matter and a 

 diminished weight, which purposes are effected by removing the 

 material as it were from the centre, and accumulating: it on the 

 cu'cumfcrence. The extremities of the humerus, as well as of all 

 cylindrical bones, are much larger than the middle portion, which 

 is for the purpose of aftbrding a greater surface for the articula- 

 tion of the joints, and the insertion of muscles to mechanical 

 advantage. This extension of surface, however, is procured 

 without any increased weight ; for there being but little danger 

 of fracture at the ends of bones, great strength is not there re- 

 quired. The bony case is therefore much thinner than in the 

 middle of the bone, and tlie internal part is filled with the can- 

 celli, or bony cells, which contain the marrow. The lower 

 j>ortion of the humerus forms a very important joint, viz. that of 

 the elbow, which in man admits of considerable rotatory motion ; 

 but in the horse, as lateral movement is not required, the action 

 of the joint is limited to one direction, backwards and forwards, 

 and thus dislocation never takes place. 



The Forearm is comjiosed of two bones, the radius and the 

 ulna. In man, both bones offer separate surfaces for articulation 

 with both the elbow and the wrist, or carpal joint, by which 

 means the arm possesses a rotatory motion ; but, in the horse, 

 this not being required, the strength of the limb is concentrated 

 in the radius, and the ulna serves merely as a powerful lever for 

 the attacliment of muscles, and the security of the elbow joint. 

 The radius is therefore a strong cylindrical bone, whilst the ulna 

 is large at the upper part, which rises above the radius, and is 

 attached to it, and gradually tapers downwards, but does not 

 reach the knee. 



The Carpus, or, as it is commonly termed in the horse, the 

 knee, corresponds with the human wrist, although apparently so 

 different. It is composed of seven bones in the hoi*se (one less 

 than in man), A\hich are arranged in two rows, thus forming 

 three distinct joints — firstly, that between the radius and the 

 first row ; secondly, between the first row and the second ; and, 

 thirdly, between the last and the metacarpal bones. 



Each of these joints possesses considerable action, moving as 

 it were like so many hinges, the fulcra of which are placed at 

 the back parts of the knee ; the lowest joint, however, does not 

 enjoy so much latitude of motion as the others. One of the 



