90 LABORATORY MANUAL OF ANTHROPOMETRY 



II. STUDY OP LATERAL PROJECTION; CURVATURE OF THE SHAFT 



A convenient plane, to be used in projections and in general compari- 

 son, is one established by Fischer, and conveniently called the sagittal, 

 or dorso-volar, although in the natural position of the forearm, with the 

 palm upwards and the radius and ulna parallel, it is set somewhat obliquely 

 and is not perpendicular to the "volar plane," used in the study of the 

 radius. 



This plane is determined by the curved ridge that runs longitudinally 

 across the greater sigmoid notch, from the volar point of the olecranon 

 to the projecting point in the lip of the coronoid process. The plane of 

 this curve also passes approximately through the styloid process at the 

 distal end, and the bone may thus be conveniently adjusted for projection 

 by placing both the curved line and the styloid process at equal distances 

 from the plane of the paper. Using this plane the bone may be inspected 

 from the two opposite aspects, the one displaying the lesser sigmoid notch 

 the other not. For the outline of the entire bone either aspect is, of 

 course, equally serviceable, but as the features of the lesser notch are 

 used in some of the measurements, the side that shows it is to be preferred. 



5. Curvature index. A comparison of several bones, or of their pro- 

 jections, in the plane just defined, shows a striking difference in the shape 

 of the bone as a whole, due mainly to a variation in the amount of curva- 

 ture in the shaft. This may be measured upon a projection from the 

 lesser sigmoid aspect by the method indicated in Figure 33. A median 

 longitudinal line is first drawn through the proximal end of the bone to 

 serve as an axis, and this crossed by a perpendicular tangent to the lower 

 (distal) border of the articular surface of the lesser sigmoid notch. This 

 locates the point a, where this cross line intersects the outer marginal line. 

 A line is now dropped from the point a towards the distal end of the bone, 

 tangent to the slight inward curve that is always found in the outline just 

 above the distal epiphysis. The exact point of tangency is the point b, 

 and the line ab is the chord of the outer outline, the curve to be measured. 

 When this has been done the amount of curvature is ascertained by 

 measuring the longest perpendicular to the chord that can be erected within 

 the limits of the curve, and this length is expressed in terms of the entire 



, , L r xi r n • r i longest perpendicular X 100. 



chord by means ot the following formula; . ' ' . , , „ 



length of chord AE 



The result is the curvature index, the greater curve giving the larger 



number. 



6 and 7. Height of olecranal cap, and olecranal cap index. A second 



measurement obtainable from this lateral projection is that of the height 



of the olecranal cap (No. 6), the amount of projection of the olecranon 



process above the upper lip of the greater sigmoid notch. The wide 



differences that are possible in this respect are seen at once by comparing 



any human ulna, in which the projection is slight, with the ulna of almost 



