Variation in the Muscles and Nerves of the Leg in Two Genera of Grouse (Tympanuchus and Pedioecetes)

by E. Bruce Holmes

The small, short posterodorsal division penetrates the ventral surface of M. iliotrochantericus medius.

Individual Variation.—In two legs the anterior division gives a twig or two twigs to M. extensor iliotibialis lateralis. 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. 5]A), there are two separate branches (both fused with the middle division) to M. iliacus. On both sides of one specimen ([Fig. 5]A), 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. On both sides of another specimen, the anterodorsal division passes lateral to the anterior end of M. iliotrochantericus medius instead of through the femoral notch, which is lacking.

T. cupido

Individual Variation.—In three legs, the anterior division gives twigs into M. extensor iliotibialis lateralis. The dorsal division is fused proximally with the middle division in one instance. In three cases, a twig from the middle division anastomoses with the branch of the anterior division supplying M. extensor iliotibialis anticus. In the example shown in [Fig. 5]B, a twig comes off the cutaneous branch of the anterior division, perforates the ventral part of M. iliacus, and rejoins the cutaneous branch. In both legs of one specimen, the cutaneous branch of the anterior division perforates the anterior edge of M. extensor iliotibialis lateralis instead of passing between the latter and M. extensor iliotibialis anticus. The posteriormost branch of the middle division, which terminates in M. femoritibialis internus, perforates the medial part of M. vastus medialis in one leg. In another leg, one of the branches to the fused Mm. vastus lateralis and vastus medialis sends a twig into M. extensor iliotibialis lateralis.

P. p. jamesi

Individual Variation.—In three legs, the anterior branch of the anterior division is cutaneous and the posterior branch supplies M. extensor iliotibialis anticus. The dorsal division may fuse proximally with either the anterior or middle division. In one leg ([Fig. 4]B), there are two branches to M. iliacus, one associated with the anterior division and one with the middle division.

Obturator Nerve

T. pallidicinctus

Description.—The long slender obturator nerve passes along the oblique iliac crest and divides into several branches immediately before reaching the obturator foramen. One or two branches, which do not pass through the foramen, penetrate the superficial surface of M. obturator pars postica. Several small branches (variable in number and arrangement) pass through the obturator foramen and supply pars ventralis, pars dorsalis, and pars antica of M. obturator. When pars ventralis and pars dorsalis are fused, one branch perforates the proximal end of this mass and reaches pars antica. One large branch passes through the obturator foramen dorsal to the tendon of M. obturator pars postica, then turns ventrally, passing lateral to the latter; the branch passes between Mm. adductor superficialis and adductor profundus and gives twigs to each of these two muscles.