Since Gadow gives different homologues for M. obturator in two of his works (1880 and 1891), one would suspect that he had changed his opinion in the interim; however, there is no evidence that he did so. In 1880 he gives supporting evidence (quoted above) for his view; in 1891 he does not. 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. In view of this discrepancy, Gadow can hardly be considered as a supporter of the idea that the avian M. obturator is homologous with the mammalian obturator internus. The evidence is conclusive, it seems to me, that the obturator internus of Hudson is not homologous with the mammalian obturator internus. Therefore, the term obturator internus is inappropriate for the avian muscle and must be abandoned. I shall follow Howell (1938) in naming the entire obturator complex M. obturator. This term, of course, is not used in the sense in which it is used by Gadow. The use of the term obturator externus for the entire complex is avoided because it may not correspond exactly to the mammalian obturator externus. As mentioned previously, Romer considers the avian muscle to be homologous not only with the mammalian obturator externus but also with the quadratus femoris. I am following the policy of Wilcox (1948) and Berger (1952) in latinizing the term anterior, changing it to anticus. When preceded by the feminine word pars, the feminine ending is used (antica). In table 1 my terminology is compared with that of Fisher and Goodman (1955), Howell (1938), Hudson (1937), and Gadow (1891). The terminology of Fisher (1946) is identical with that of Fisher and Goodman (1955) except that in his earlier work Fisher did not describe or name M. femoritibialis externus, and M. lumbricales of his earlier work is not mentioned in his later work. The terminology of Hudson, _et al._ (1959) is identical with that of Hudson (1937) except that the manner in which the femoritibialis complex is subdivided is identical with that of Gadow (1891) and different from that in Hudson's earlier work; also the abbreviations p. ext. and p. int. are substituted in his later paper for pars anterior and pars posterior, respectively, of M. adductor longus et brevis. ACKNOWLEDGMENTS