Ramification patterns of the nerves innervating the forearm extensors in mammals and reptiles

This paper discusses muscle phylogeny based on muscle innervation and defends a new concept of nerve-muscle specificity. Some researchers argued strongly against this concept in the first half of this century. However, we think their arguments were partially based on insufficiently examined findings of the ramification manner of the radial nerve. We have dissected 140 limbs of 25 species in mammals and reptiles to examine the manners of ramification of nerves supplying the forearm extensors. The pattern of the radial nerve has been revealed to consist of consistent and inconsistent elements. The branches to the forearm extensors except for the supinator follow quite consistent patterns, while the branch(es) to the muscle is much less consistent. Comparing the ramification patterns of the nerves between mammals and lizards, it can be concluded that the radial nerve in mammals is formed by the phylogenetic path alteration of its partial nerve fibers from the pathway along the flexor side in lizards to the route in the extensor side.