450 THE ASCENT OP MAN. 



a flexor of the wrist. This soldering uudoubtedly took place because 

 the muscle was no longer required as a finger-holder. Like other organs 

 that after playing a part of considerable functional importance have 

 come from change of habit to be of but little value, it shows the most 

 astonishing tendency to variation. Not a week passes in a large dis- 

 secting room that some curious anomaly is not found in this muscle. 

 Sometimes it is seen almost in its jirimitive condition, the i^almar fascia 

 being comparatively movable and thepalmaris longiis having some effect 

 upon the flexion of the fingers : oftener it unites wholly or partiall}^ with 

 some portion of the pronato-flexor mass or disappears altogether. The 

 disappearance is usually only ajiparent, however. Regressive struc- 

 tures rarely disappear totally, for on careful search a strip of fascia can 

 usually be found that represents the atrophied and aborted organ. 



Since these two examples differ in that the first represents the devel- 

 opment of a new muscle while the second is the atrophy of an old one, 

 we ought to find racial differences corresponding to these two condi- 

 tions. Our studies of racial anatomy are as yet far from sufficient to 

 give us complete information upon these points, and I would especially 

 avoid generalizing upon too meager dat;>. It has however appeared 

 to me that in negroes the palmaris Jongus is more inclined to assume its 

 l)rimitive type — that is, is less likely to vary — while the long flexor of 

 the thumb is on the contrary more inclined to be partially, if not wholly, 

 united with the deep flexor of the fingers. 



Connected intimately with the hand are the other portions of the 

 thoracic limb that carry it from place to place. Here again we may 

 note many points indicating a progressive develoj)meut of the member. 

 When the arm is naturally and easily bent at the elbow it does not 

 carry the hand to the shoulder, as might be expected, but towards the 

 mouth. The reason for this is that the articular surfaces of the elbow- 

 joint are not cut horizontally across the axis of the humerus, but inclined 

 at an angle of about 20°. This obliquity does not occur in the ftptus and 

 is less in Bushmen, Australians, and the anthropoid apes. It is associ- 

 ated with another peculiarity; indeed, may be said to be caused by it. 

 This is a twisting of the humerus on its long axis, which occurs markedly 

 in the higher races. If we hold up endwise the humerus of a European 

 we see that the longest diameters of the upper and lower ends very 

 nearly coincide. In the negro we find the lower diameter turned more 

 towards the body, still more in the anthropoid apes, and again more as 

 we descend the scale. Embryology teaches that the humerus was for- 

 merly set so that the hollow of the elbow looked towards the body 

 rather than forward, and it seems therefore that as the functions of 

 the limb became more various, the lower end of the bone gradually 

 twisted outward around the long axis until its diameter described a 

 considerable arc. This turned the hand with the palm to the front, ex- 

 tended its range, and adapted it for a wider usefulness. Greater twist 

 is found in the right humerus than in the left and in the humeri of 



