104 MECHANISM OF THE BONES. 



A. Each of them is composed, that is, the up- 

 right limbs, of three bones, the same number as in 

 the arm : the two lower, called the tibia, and fibula, 

 between the knee and the ankle, supporting a single 

 bone which joins immediately to the body, and is 

 called the femur or thigh bone. But notwithstand- 

 ing this general resemblance between the two sets of 

 limbs, there are some remarkable differences, which 

 are adapted still further to increase our devout admi- 

 ration of the wisdom and intelligence exhibited in 

 the animal frame. 



Below the knee the limb swings backwards ; be- 

 low the elbow, it is the reverse. We can assign no 

 natural reason why limbs, which otherwise are so 

 similar, should have been hung so differently. But 

 we see the advantage, — for let a person only reflect 

 on the uncomfortable effects of an opposite arrange- 

 ment. 



The upper single bone in the lower limbs is much 

 stronger than the upper single bone corresponding to 

 it in the arm. Indeed, the thigh bone is the strong- 

 est bone in the frame. We observe the design. 

 This bone has to sustain the weight of the body, and 

 the additional weight of every burden we carry. 



It is united to the hip by a ball and socket joint, 

 as is the upper bone of the arm at the shoulder blade. 

 But the socket at the shoulder is shallow ; while that 

 of the hip is the deepest in the whole body. "This/' 

 says Dr. Paley, " agrees well with the duties assign- 

 ed to each part. The arm is an instrument of mo- 

 tion principally, if not solely, and accordingly re- 



