E. Bruce Holmes

“ The dorsal division may fuse proximally with either the anterior or middle division, thus appearing to be a branch of one of these divisions. In one leg (Fig. 5A) , there are two separate branches (both fused with the middle division) to M. iliacus. On both sides of one specimen (Fig. 5A) , the anteriormost branch of the middle division, which supplies M. extensor iliotibialis lateralis, gives off a twig that anastomoses with the branch of the anterior division that supplies M. extensor iliotibialis anticus. ”

“ After describing (1891:173) how the origin of M. obturator in bird ancestors presumably migrated from a location outside the pelvis to a position inside the pelvis prior to the meeting of the pubis and ischium external to the muscle, he states: "Eine ähnliche Entwicklung ist für den Obturator internus der Säugethiere anzunehmen, welchem der M. obturator der Vögel entspricht." A similar development in mammals is impossible, owing to the different relationship of the muscle to the pelvic bones in this class. Gadow says nothing more about the mammalian homologue of M. obturator. ”

“ The lumbosacral plexus and nerves of the leg in several specimens that show variations are illustrated.
Considerable individual variation was found in both the muscles and the nerves of the leg of the species studied. Certain muscles were more variable than others. Mm. flexor digitorum longus, obturator, caudofemoralis, and extensor hallucis longus showed the greatest number of variations. Mm. vastus medialis, femoritibialis internus, flexor perforatus digiti III, extensor brevis digiti III, and abductor digiti IV did not exhibit any variations considered significant. ”

“ The stimulus for a longer muscle, has been the same, resulting in the extension of origin to within the pelvis of the externus in birds and the internus in mammals, but the obturator internus is an extension of a part of the gemellus mass and this does not occur in any vertebrate class but Mammalia. ”

“ In most specimens there was as much variation between the muscles of the right and left legs of one individual as there was between individuals. The same was true for the nerves, except for the lumbosacral plexus, in which there was no significant variation between the right and left sides of any individual. The peroneal and obturator nerves varied less than the other nerves. ”

“ It remains to be determined how many specimens need to be studied in order to obtain a fairly accurate picture of variation.
Comparison with Other Studies of Innervation
I accept the following concept of muscle-nerve relationship. All muscles of the pelvic limb of birds have developed phylogenetically [Pg 453] 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) . ”

“ Of the 50 muscle variations seven were found only in T. pallidicinctus (eight legs) , 16 were found only in T. cupido (nine legs) , and ten were found only in Pedioecetes (six legs) . Two were found in both species of Tympanuchus (but not in Pedioecetes) . Fifteen were found in both Tympanuchus and Pedioecetes; of these, five were found in all three species studied, eight were shared by T. pallidicinctus and Pedioecetes, and two occurred in T. cupido and Pedioecetes.
Nerves
The lumbosacral plexus, femoral nerve, sciatic nerve, and tibial nerve all showed numerous individual variations. ”