THE HAUNCH AND THIGH. 85 



There is this important difference, however, in the construction of 

 these correspondent articulations : the os humeri is placed beneath 

 the scapula, in such a situation that the weight of the body comes 

 directly upon its head ; whereas, in consequence of the head or 

 articulatory part of the os femoris, instead of forming the summit of 

 the bone, being laterally placed, at a right angle to the shaft of the 

 bone, the weight is transmitted, not perpendicularly upon the os 

 femoris, but in an oblique or indirect line. One reason for this ap- 

 pears evident, in the different relations to the body existing between 

 the shoulder and hip, the latter being in consolidated connexion 

 with the body itself, the former attached only through the interven- 

 tion of muscle. The lateral position of the hip joint serves, in a 

 measure, to compensate for the want of that elasticity and spring 

 which the shoulder derives from its muscular attachments, to coun- 

 teract or mitigate any shock or concussion the limb may sustain in 

 action, such as from jumping, &c. There is another and a greater 

 advantage, however, resulting from this position of obliquity. At 

 the time that the weight of the body is pressing with its greatest 

 force upon the hip joints, from the pressure being sideways instead 

 of perpendicular, their motions under the weight are, compara- 

 tively, easily carried on — the work of progression is saved that 

 hinderance and difficulty which would have attended the direct 

 imposition of weight upon these joints, to say nothing about the 

 friction and wear from concussion the joints themselves must 

 necessarily have sustained. A third reason for placing the head 

 of the os femoris in an angular position, and setting it off from the 

 shaft or body of the bone by means of a neck — for so the inter- 

 vening portion of bone is called — is, that the joints might possess 

 an enlarged sphere of motion. In the fore extremity, the scalpula 

 itself being a moveable bone, the humerus did not require this ; 

 but in the hind, the pelvis being a fixture to the trunk, it was 

 necessary to confer as much mobility upon the hip joint as was 

 compatible with the strength required in it to carry the weight of 

 the body and to guard against any risk of dislocation. Had any- 

 thing like the force resulting from weight and action been in 

 operation in the fore extremity the same as in the hind, the 

 shoulder joint could never have admitted of the loose and super- 

 ficial construction it at present, for the sake of motion, enjoys. It 



