osteometry; the measurement of the bones 93 



more the opening of the notch is elevated (Fig. 33, I and II). Should 

 this look downwards the intersection would be below and the angle would 

 be given a minus value. 



On an average, in modern races, this angle has a value of 15-20°; 

 but an angle of 32° has been recorded. The value of this angle which, 

 from the two points involved, is termed the olecrano-coronoid, is directly 

 concerned in the question of the angle formed at the elbow during the 

 extension of the arm, since a complete extension to 180° is more easily 

 possible, other things being equal, when the olecrano-coronoid angle is 

 large, that is, when the notch is directed upwards. This possibility of 

 complete extension is, however, dependent upon other factors also, for 

 example, the depth of the olecranon fossa, or a slight forward cant of the 

 olecranon process as a whole; so that an unusually deep fossa, or perhaps 

 a perforation of the bone (supra-trochlear foramen), may compensate 

 for a moderately low position of the greater sigmoid notch, and still 

 render a complete extension possible. When, however, the angle is very 

 small, and the notch has little or no upward direction, a complete exten- 

 sion, even with these compensations, is quite impossible. This is the 

 condition in Homo neandertalensis so far as known; the olecrano-coronoid 

 angle is low, and the extension of the arm is incomplete, the bones, when 

 articulated, forming an angle of 160-165° when fully extended, so that, in 

 the flesh, allowing for the space taken up by the soft parts, the amount of 

 extension must have been even less. 



In the lower monkeys the olecrano-coronoid angle is very low, in some 

 cases even negative (notch pointed downwards) and it would seem that 

 here also a complete extension is impossible. Many human races, on 

 the other hand, both high and low, such as the Central Europeans and 

 the Australians, possess a high angle, and presumably have the power 

 of complete extension. Definite statements on this point cannot be 

 made from lack of sufficient data, and more detailed study, not only upon 

 the bones but more especially upon the living, including all races and both 

 sexes, are a pressing need. 



III. STUDY OF THE VOLAR PROJECTION 



This projection is that of the bone when rotated about its longitudinal 

 axis exactly 90° from its former position, showing the curved longitudinal 

 ridge that crosses the greater sigmoid notch as a straight line. As the 

 former position was not strictly lateral, though called so for convenience, 

 so this position is not quite volar, but in the normal position of an ex- 

 tended arm is set at nearly 45° to the "volar plane" of the radius, de- 

 scribed in the next section. Like the aspect previously used, however, 

 it best shows certain essential peculiarities and has the advantage of being 

 consistent with it. 



From this aspect the entire shaft is seen to possess a very slight S- 

 curve, but it is difficult to measure, and thus far has yielded no important 



