MECHANISM OF THE INFERIOR EXTREMITIES. 239 



gard to the spine, prevents us from falling to one side, and, at 

 the same time, brings the lower extremities immediately in a 

 line with the spine. 2d. The length of the neck of the os fe- 

 moris, and the size of its condyles. 3. The articulation of the 

 knee, which permits the leg to be brought into a line with the 

 os femoris, a position impracticable in quadrupeds. 4th. The 

 foot being articulated at a right angle with the leg, and having 

 its tarsus and metatarsus so well developed. 5th. The predo- 

 minance of the transverse diameter of the thorax over the ver- 

 tical, which, with the great length of the clavicle, and the 

 shape of the scapula, unfit the latter for assisting much in pro- 

 gression. 6th. The shape of the hand, calculated to seize upon 

 objects, but from the length of its phalanges not suited to sus- 

 tain the body. 7th. The mode of articulation at the wrist, 

 which, from its mobility and weakness in the direction to which 

 the weight of the body would be applied to it, could not be 

 brought to support it advantageously. And, lastly, the great 

 disproportion of length, in the adult, between the upper and 

 lower extremities, when an attempt is made to walk like the 

 quadruped. 



In considering the skeleton of the very young child, it is 

 worthy of remark how closely its mechanism, with the excep- 

 tion of the head, corresponds with the habits of early life. 

 A spine, nearly straight, and a pelvis, the lateral diameter 

 of whose cavity is so small that the transverse base of 

 support is much diminished, render erection inconvenient. 

 Low T er extremities shorter in proportion than the upper ones, 

 having thigh bones nearly straight; also, the articulations 

 of the knee not admitting of a full extension of the leg. 

 All these circumstances prove that the quadruped position, 

 inconvenient and intolerably irksome when continued for a 

 length of time in the adult, is natural to the young infant. 



The space between the ossa femorum, produced by the breadth 

 of the pelvis and the length of their necks, and, therefore, always 

 considerable above, varies below in different individuals. A cer- 

 tain distance at the latter point seems to be indispensable to con- 

 venient and graceful progression. Thus, when it is in excess, it 

 produces the deformity called bandy legs, and causes a totter- 



