504 THE MECHANICAL FUNCTIONS. 



each other, so as to occupy a situation as nearly 

 as possible underneath the weight which the 

 limb has to support. 



The radius and ulna, which are the two bones 

 of the fore arm, although completely separate at 

 an early period of growth, soon unite to form 

 but one bone. This union begins at their lower 

 end, and proceeds upwards to within a short dis- 

 tance from the top, where a separation may still 

 be observed in the processes which project from 

 that end, forming for some way down a distinct 

 suture. This union of the two bones must, of 

 course, preclude all rotatory motion ; but it is 

 calculated to give the joint great security : 

 and this appears to have been the main object 

 in the conformation of the whole limb. The 

 same process of consolidation takes place in the 

 hind leg, between the tibia and the fibula, which 

 are so completely united, as to afford scarcely 

 any trace of their having been originally se- 

 parate. 



The carpus and the tarsus are both of very 

 limited extent, and consist of a smaller number 

 of pieces than usually occur in these joints. 

 The consolidation of parts is most conspicuous 

 in the succeeding division of the limb, namely, 

 that constituting the metacarpus in the anterior, 

 and the metatarsus in the hind extremity. In 

 either case we find it consisting, not of five 

 bones, as in the more highly organized carni- 



