Berger (1952), in his description of the Black-billed Cuckoo (_Coccyzus erythrophthalmus_), also divides the obturator complex into an obturator internus and an obturator externus; the latter he subdivides into a dorsal and a ventral part. He states (p. 530) that he did not find any measurable differences in myology between _C. erythrophthalmus_ and _C. americanus_. In order better to compare this arrangement with that in _Tympanuchus_, I have examined two specimens of _C. americanus_. My findings in the latter differ from Berger's description (p. 541) in one respect. Whereas Berger states that the dorsal and ventral parts of M. obturator externus are distinct except at their origin, I find them fused for their entire length; the muscle fibers that connect these two parts lie deep to the tendon of M. obturator internus. The origin of all parts of the complex in _Coccyzus_ is similar to that in _Tympanuchus_. The only notable difference in configuration is that the part in _Coccyzus_ that appears to correspond to the obturator externus of Hudson, _et al._ (1959) is not separate from the remainder of the extrapelvic part of the muscle. Berger (1952) considers all parts of the muscle having an extrapelvic origin to make up the obturator externus. It appears to me that the dorsal part and a part of the ventral part of the obturator externus of Berger correspond to the extrapelvic fleshy part of the obturator internus of Hudson, _et al._ From my limited study, it seems to me to be desirable to recognize four subdivisions of the obturator complex, for which I propose the terms pars antica, pars dorsalis, pars ventralis, and pars postica. These parts exhibit various degrees of fusion in different groups of birds and some parts appear to be absent in certain birds. A study of a wide variety of birds will be required to determine whether or not a subdivision into the four parts proposed here is suitable for birds as a whole. Applying these terms to _Coccyzus_, pars postica is equivalent to the entire obturator internus of Berger (1952). Pars dorsalis is apparently equivalent to the dorsal part of Berger's obturator externus. The ventral part of the obturator externus of Berger represents the fused pars antica and pars ventralis. The main parts of the obturator muscle appear to be pars postica and pars antica. Pars dorsalis and pars ventralis are more variable; in _Coccyzus_ these two parts are closely associated with pars antica whereas in _Tympanuchus_ they are most closely associated with pars postica. Apparently pars dorsalis and pars ventralis may be absent in some birds. _T. pallidicinctus_