Fisher (Fisher, 1946; Fisher and Goodman, 1955) considers the muscle here termed M. femorocruralis as an accessory head of M. flexor cruris lateralis. The two muscle units in question are closely associated; they insert broadly on opposite sides of a common tendinous raphe. Howell (1938:73) considers this to be a secondary fusion of unrelated muscles. Romer (1927:366) states that in the chick embryo M. femorocruralis is in reality a shank muscle that migrates into the thigh during development. Therefore, Fisher's usage of a single name for these two unrelated muscles is unsatisfactory. I am using Howell's terminology in which the name flexor cruris lateralis represents the main head only of Fisher's M. flexor cruris lateralis and the name femorocruralis represents Fisher's accessory head.
Gadow (1891) divides the obturator complex into two muscles (or muscle groups), which he terms M. obturator and Mm. accessorii M. obturatoris. He states that the former is homologous with the mammalian obturator internus and the latter with the obturator externus. Hudson (1937), accepting Gadow's homologies, renamed these muscles M. obturator internus and M. obturator externus. Nearly all subsequent workers have followed Hudson's terminology, with its implication that these muscles are homologous with the mammalian muscles of the same name. Howell (1938) is an exception. He points out (pp. 78, 79) that the obturator internus of Hudson is homologous with the obturator externus of mammals. His evidence is convincing: "In origin the obturator is somewhat suggestive of the mammalian obturator internus, for which it has uniformly been mistaken. That the latter interpretation is incorrect, however, is attested by the facts that it receives twigs of n. obturatorius within the pelvis, passes _through_ the obturator foramen rather than dorsal to the border of the ischium, and it is segregated from any muscle with tibial innervation. Insertion has shifted only to a slight and unimportant degree as compared with that of the mammalian obturator externus, and beyond question it is the equivalent of that muscle. 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." Howell applies the term M. obturator to the entire obturator complex.