Anatomical and descriptive study of the radial extensor muscle (M. extensor carpi radialis)

The M. extensores carpi radiales have been studied in detail in humans. The aim of this study was to carry out a comparative anatomical study of these muscles using four species--rabbit, cat, dog and sheep--and to propose a 'systematization' in a few standard models according to the morphological variations seen. In these species, there is marked morphological evolution, with two muscles in humans, one in sheep and a more or less distinct division of the muscle in the rabbit, cat and dog. Examination of the vascularization and nerve supply enables us to determine degrees of division in species with similar muscle morphology. Thus we were able to distinguish three morphological types which allow us to infer the morphological evolution of the M. extensores carpi radiales and to estimate the point at which one muscle became two. However, there is a strong chance that some process of convergence may have occurred, and in pentadactyl species many elements represent the plesiomorphis and are therefore of little use in constructing a classification on the basis of evolution.