MECHANISM OF THE INFERIOR EXTREMITIES. 235 



About the fifteenth year, the bones of the lower extremities 

 have very nearly the same forms as in the adult: they are all fully 

 ossified, with the exception of their extremities not being fused 

 or joined to their bodies; but still in the state of epiphyses, and, 

 therefore, separable either by boiling or long-continued macera- 

 tion.' Exclusively of this condition, which sometimes remains to 

 the twentieth or tWenty-fifth year, the epiphyses are as fully os- 

 sified as at any subsequent period of life. 



SECT. V. ON THE MECHANISM OF THE INFERIOR EXTREMITIES IN 



REGARD TO STANDING. 



The os femoris is well adapted by its shape and position to 

 the erect attitude. The curvature which its body makes in 

 front has the effect of advancing the lower part of it, and there- 

 by keeping it in a line with the centre of the trunk; but if it had 

 been perfectly straight, the erect position would have been main- 

 tained with great difficulty, owing to the centre of the trunk 

 being in advance of this bone. Under the latter circumstancea, 

 an incessant tendency to fall forwards would have manifested 

 itself, which could have been obviated only by flexing the ossa 

 femorurn very much at the hip joint, or by keeping one foot al- 

 ways in front of the other. Even under the actual arrangement 

 of the skeleton, when muscular support is withdrawn from it sud- 

 denly, it falls forwards, owing to the weight of the parts anterior 

 10 the spine being greater than that of the parts posterior to it. 

 When muscular action is weakened or badly regulated, the same 

 tendency to fall forwards is manifested : children continually 

 tumble in that direction: a person in a state of intoxication, 

 somewnat short of the entire loss of locomotion, not being able 

 to sustain the trunk of the body erect by the muscles of the 

 back, inclines forwards, and would be precipitated to the ground, 

 were it not that at this crisis one leg is involuntarily advanced, 

 so that the base of support is much augmented. But if the in- 

 dividual attempt to walk, the continued necessity of keeping a 

 large basis of support to prevent the body from falling forwards, 

 urges him into a slow 7 running or trotting gait. 



The arrangement of the whole upper extremity of the os fe- 



