82 NATURAL THEOLOGY. 



Another no less important joint, and that also of the gin- 

 giymu3 sort, is the ankle ; yet though important — in order, 

 perhaps, to preserve the symmetry and lightness of the 

 limb — small, and on that account more liable to injury. 

 Now this joint is strengthened, that is, is defended from dis- 

 location by two remarkable processes or prolongations of the 

 bones of the leg, which processes form the protuberances 

 that wc call the inner and outer ankle. It is part of each 

 bone going down lower than the other part, and thereby 

 overlapping the joint : so that if the joint be in danger of 

 slipping outward, it is curbed by the inner projection, that is. 

 that of the tibia ; if inward, by the outer projection, that is, 

 that of the fibula. Between both, it is locked in its position. 

 I know no account that can be given of this structure, ex- 

 cept its utility. "Why should the tibia terminate 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 slioul- 

 dei', compared with the joint at the hij'), though both ball- 

 and-socket joints, discovers a difierence in their form and 

 proportions, well suited to the different offices which the 

 limbs have to execute. The cup or socket at the shoulder 

 is much shallower 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 shal- 

 lowness of the socket at the shoulder, and the yieldingness 

 of the cartilaginous substance v/ith 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 M'ants. 

 Wheieas the lower limb forming a part of the columu of 

 the body — having to support the body, as well as to be the 

 means of its locomotion- — firmness was to be consulted as 



