NATURAL THEOLOGY. 123 



at its lower extremity, with a double end, and the 

 fibula the same — but to barricade the joint on 

 both sides by a continuation of part of the thickest 

 of the bone over it ? The joint at the shoulder, 

 compared with the joint at the lii^j, though both 

 ball and socket-joints, discovers a difference in 

 their form and proportions, well suited to the dif- 

 ferent offices which the limbs have to execute. 

 The cup or socket at the shoulder is much shal- 

 lower and flatter than it is at the hip, and is also 

 in part formed of cartilage set round the rim of 

 the cup. The socket, into which the head of the 

 thigh-bone is inserted, is deeper, and made of 

 more solid materials. This agrees with the duties 

 assigned to each part. The arm is an instrument 

 of motion, principally, if not solely. Accordingly, 

 the shallowness of the socket at the shoulder, and 

 the yieldingness of the cartilaginous substance 

 with which its edge is set round, and which in 

 fact composes a considerable part of its concavity, 

 are excellently adapted for the allowance of a 

 free motion and a wide range, both which the 

 arm wants. Whereas, the lower limb, forming a 

 part of the column of the body, — having to sup- 

 port the body, as well as to be the means of its 



securely. But before the weight of the body is brought perpendicu- 

 larly over the foot, there is no danger to the joint, because there is 

 no strain upon it. Just in proportion as the advancing body be- 

 gins to bear upon it do the bones take that position, in which 

 they are as firm as in the knee-joint itself, admitting only the mo- 

 tion of a hinge. 



