134 LABORATORY MANUAL OF ANTHROPOMETRY 



(d) The line of inclination of the inner condyle, which is that of 

 the steel needle; found by connecting the two points already 

 located in the projection. Naturally these may be placed 

 anywhere along the needle, but the line is more accurate 

 the farther apart they are. JK. 

 The three angles above listed are thus constructed, and now have 

 merely to be read off, thus : — 



1 Retroversion angle; the angle JDG is measured for this, after 

 which 90° are subtracted. This gives the value of the true 

 retroversion angle, LMD, which is that between the axis 

 of the retroverted proximal end (at right angles to the inclination 

 of the face of the condyle) and the diaphysial axis. 



2 Inclination angle HLK, the angle of inclination of the face of 

 the inner condyle, compared with that of the mechanical 

 axis of the entire bone. Here also 90° are to be subtracted. 



3 Biaxial angle; that between the two long axes here used, 

 mechanical and diaphysical, HAG. Its value is that of the 

 difference between the two preceding angles, of reversion and 

 inclination. Thus, in the diagram here shown, Fig. 38, the 

 first is 25°, the second 21°, and the biaxial 4°. 



The reason for using the plane of inclination of the proximal articu- 

 lar surface is that it is at right angles to the axis of the short proximal part, 

 the angle of retroversion of which is sought, and that it can be placed in 

 a projection with considerable precision, while there is little to use in 

 placing a definite axis to this short part. This large surface is, however, 

 at right angles to the axis sought, and hence its angle may be measured 

 and then reduced by 90°. Should the investigator so desire, he might 

 ascertain the axis of each part as he best can by estimation, fix steel 

 needles to both, and measure the angle between them direct on the bone, 

 as in similar cases. 



The value of this retroversion angle has been found to vary from 0° in 

 an ancient French skeleton to 30° in a California Indian, but is usually, 

 in European skeletons, between 15 and 20°. The diagram given here 

 where the angle of retroversion is 25°, is taken from an Australian. 



A considerable retroversion of the tibia is the usual fetal condition, 

 even in Europeans, and is retained during infancy. In other words it is 

 a universal human condition of human tibiae at birth, and is retained by 

 certain of the lower races, but is generally outgrown by Europeans. 



4. Angle of torsion; as with such bones as the humerus and the femur, 

 this angle is made by the lateral axes of the two ends of the bone, pro- 

 jected upon each other in a bone held perpendicular to the paper. The 

 proximal axis passes through the two condyles, at right angles to what 

 is judged to be the sagittal plane, and the distal axis is drawn across the 

 articular surface from the point of the inner malleolus to the opposite 

 side, as in the case of the radius. Little has been done with this angle 



