An attempt to the method of investigations and interpretations of asymmetry in long bones

Abstract

The author has investigated asymmetry of 109 ♂ and 100 ♀ pairs of upper arm bones. Four from 19 taken into account characters, were areas of perpendicular projections of humerus and its parts into frontal plane. Arcas of projections of shaft, upper and lower epiphysis and sum of them were measured according to the author's method. Next four characters were indices calculated from above areas: epiphyseo-diaphyseal, upper epiphysis, lower epiphysis and total massiveness index. Other characters were linear, measurements, condylo-diaphyseal angle and relief on the muscle attachment surfaces. Comparison of our results with the data of other authors (concerning only with some linear measurements and weight) has shown a similar pattern of asymmetry in each compared character.

Right-sided asymmetry is distinctly pronounced (significant differences between mean values for right, and left side, higher relative asymmetry A_w — see tab. 3; high frequency of right-sided asymmetry see tab. +) in: horizontal dimensions of upper epiphysis, breadth and length of shaft and vertical plane of lower epiphysis. This is also true for characters expressing general size of bone: total area of projection, massiveness, maximum and total length. Asymmetry of the shaft is the main factor of whole bone asymmetry, they are strongly correlated (r ≈0.85).

Males have more asymmetric epiphyses, and less asymmetric shaft of humours, than females. Relative asymmetry is positively correlated with individual variability of characters (greatest asymmetry — greatest variability, r = 0.60).

Variability of individual differences, in each case, do not precede individual variability of examined character. There is no strong correlation between decree of asymmetry and morphology of bone (its size, proportions, massiveness, relief of muscle attachment surfaces).

After discussing above results the author has come to following conclusions: The main factors of skeletal asymmetry are — 1. hereditary determined “plasticity” of bones and 2. differences between frequencies, directions and quantities of functional stresses. Second group of factors induces changes in morphology of bones which are magnifying moments of muscle tension. However action of muscles attaching to the bone in question is not the main function responsible for these changes, because there is no distinct asymmetry in relief of muscle attachement surfaces (see tab. 5). Morphology of bone and function of muscle are in part independent, but they act complementary forming full dynamical asymmetry of extremities,