For ease of description I have coined terms for the major divisions of the femoral and sciatic nerves.
Muscles
My terminology follows that of Fisher (1946) and Fisher and Goodman (1955) except for Mm. femoritibialis externus, flexor cruris lateralis (accessory head), and obturator internus et externus. Fisher (1946:547) states that most of his names for the hip and thigh muscles are those of Howell (1938) and the names for the shank and foot muscles are those of Hudson (1937). Fisher deviates, without explanation, from Howell's terminology in respect to Mm. vastus medialis and femoritibialis internus, M. caudofemoralis, M. flexor cruris lateralis, and Mm. obturator internus and obturator externus. Fisher's synonymy of these muscles (1946: table 42) is in error. Fisher understandably deviates from Hudson in respect to Mm. extensor brevis digiti III and extensor proprius digiti III (see Holmes, 1962), although Fisher's synonymy is in error here. See my table 1.
I am not using Fisher and Goodman's term femoritibialis externus; this muscle is here considered as a part of M. vastus lateralis. A great deal of confusion surrounds the terminology of the muscle complex here termed Mm. vastus lateralis and vastus medialis. Hudson (1937), Hudson, et al. (1959), Fisher (1946), and Fisher and Goodman (1955) have used different terminology for this complex. Most of the confusion stems from Gadow's (1891) unclear description of this complex, which he subdivided into two units termed Mm. femori-tibialis externus and femori-tibialis medius. Many birds have three parts to this complex. It is difficult to determine how to apply Gadow's two terms to these three parts. As nearly as I can determine, the correct method is that of Hudson, et al. (1959); but because Gadow's terms have been used in different ways (even by the same worker), it seems best to abandon these terms. Berger (1956:272) believes that the muscle unit that Fisher and Goodman term M. femoritibialis externus represents a head of M. vastus lateralis; I am accepting his opinion. For the three parts of the complex under discussion, I am using the terms M. vastus medialis and M. vastus lateralis pars lateralis and pars postica.
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.
Romer (1927), studying the development of the thigh musculature in chick embryos, concluded that the entire obturator complex is homologous with the mammalian obturator externus plus quadratus femoris. He considered the avian M. flexor ischiofemoralis to be the homologue of the mammalian obturator internus.
Gadow, in his work on the ratites (1880:34), states that M. obturator (obturator internus of Hudson) cannot be homologous to the mammalian obturator internus, but must represent the obturator externus. His reasoning is as follows: "Als M. pectineus kann man diesen Muskel nicht auffassen, da er auf der Aussenfläche des Trochanter major inserirt, ferner auch nicht als M. obturator internus der menschlichen Anatomie, da er nicht vom Plexus ischiadicus, sondern vom Plexus cruralis aus innervirt wird. Seiner Innervation und Insertion nach wäre er nur mit dem M. obturator externus zu vergleichen, wobei er seinen Ursprung im Verhältniss zum Menschen nur bedeutend weiter auf das Os ischii und Os pubis distalwärts ausgedehnt hätte und so allerdings der Lage nach mit Ausnahme seines Insertionsdrittels ein 'internus' geworden wäre."
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]
I gratefully acknowledge the generous help of Professor A. Byron Leonard, under whose guidance this study was conducted and thank Professor E. Raymond Hall, Professor Howard A. Matzke, and Dr. Irwin Baird for numerous helpful suggestions and criticisms.
For help in collecting specimens I thank J. R. Alcorn, W. C. Glazener (through the courtesy of the Texas Game and Fish Commission), Dr. Harrison B. Tordoff, Jerry Tash, William Brecheisen, and Louis Brecheisen. I thank also Edwin Gebhard of the Kansas Forestry, Fish and Game Commission for help in locating the Lesser Prairie Chickens.