A study of the extensor tendons of the hand from point of view of evolution

Abstract

IntroductionBoth anatomists and the surgeons need to have knowledge of anatomy of extensor muscles and their variations but the analysis of characteristics of each of these muscles can also improve our understanding of evolution of modern human beings. Methods100 upper limbs preserved in 10% formalin were dissected to study the extensor muscles on the dorsum of forearm and hand. Results28% incidence of variation was observed. Variant muscles such as extensor carpi radialis tertius (4%), extensor digitorum brevis manus (2%) and extensor medii proprius(4%) were observed. Duplication and triplication of extensor digitorum communis tendons to the 2nd, 3rd and 4th digits was noted. A 28% incidence of absence of extensor digitorum communis tendon to the little finger was observed. DiscussionPresent study attempted to explain the presence of these extra muscles on the basis of their actions. Increased supination and pronation movements have been associated with more number of muscles/tendons in the extensor carpi radialis muscle and could explain the formation of extensor carpi radialis tertius muscle observed in the present study. The need to extend wrist and throw an object in a precise direction which was the need of the primate evolving to be the human being, could explain the extra extensors seen over the wrist and digits. A very well developed extensor mechanism is needed for precise functioning of the hand. The present study attempts to link together the functioning of individual extensor muscles to the trajectory of events involved in evolution of primates.