I accept the following concept of muscle-nerve relationship. All muscles of the pelvic limb of birds have developed phylogenetically from either the dorsal extensor muscle mass or the ventral flexor muscle mass. The former was (at least originally) supplied by only the femoral and peroneal nerves ("dorsal" nerves), the latter by only the obturator and tibial nerves ("ventral" nerves). The best guide for determining which muscles are phylogenetically dorsal and which are ventral seems to be their embryogeny (as shown in the studies of Romer, 1927, and Wortham, 1948). In the phylogenetic changes undergone by the muscles under consideration, the innervation may have changed in some instances, although this is less likely to occur than changes in the attachment or function of the muscles. If a change in innervation has occurred, it would be more likely to be a change from one dorsal nerve to the other or from one ventral nerve to the other rather than from a dorsal nerve to a ventral one or _vice versa_. Thus, in my opinion, a report of a dorsal muscle supplied by a ventral nerve, or _vice versa_, should be viewed with suspicion until it is verified. I suspect that many previous workers have ignored this concept of muscle-nerve relationship, or else do not accept it, since they report, without comment, dorsal muscles (as determined embryologically) innervated by ventral nerves, or _vice versa_. Owing to the intimate association between the proximal parts of the tibial and peroneal nerves, the true relationship may be difficult to determine. I suspect that this relationship has been misinterpreted by a number of workers. I found in _Tympanuchus_ and _Pedioecetes_ a branch of the tibial nerve that is closely associated with, and distributed with, the peroneal nerve and has been mistakenly considered a part of the peroneal nerve by some workers. In the study here reported on, I have found no definite exceptions to the expected innervation. The only possible exception is an extra branch, which could not be traced to its origin, supplying M. extensor iliofibularis in one leg. Thus my study of innervation agrees with the embryological determination of the (phylogenetic) dorsal and ventral muscles and lends strong support to the above-stated concept of muscle-nerve relationship. I have compared my findings on the nerves with those of other workers, who have studied the nerves with a varying degree of thoroughness. The important differences in innervation between these studies and the present one are discussed below.