FIG. 20. A-D. Dorsal views of M. iliotrochantericus medius, showing its relationship to femoral notch. × 1. In D, note absence of femoral notch and location of branch of femoral nerve. A. _Tympanuchus pallidicinctus_ 2L. B. _T. cupido pinnatus_ 4L. C. _Pedioecetes phasianellus jamesi_ 1L. D. _T. pallidicinctus_ 3L. E. Medial view of distal end of M. flexor cruris medialis of _P. p. jamesi_ 4L. × 1. Part of insertion is covered by medial collateral ligament. F,G. Lateral views of posteroproximal corner of M. extensor iliotibialis lateralis (removed from specimen). × 1. F. _T. pallidicinctus_ 2L. G. _P. p. jamesi_ 3L. H,I. Dorsolateral views of M. piriformis. × 1. H. _P. p. jamesi_ 1L. I. _T. cupido attwateri_ 1L. J. Lateral view of M. caudofemoralis pars caudifemoralis (removed from specimen) of _T. c. pinnatus_ 4L. × 1. K. Lateral view of extrapelvic part of M. obturator of _T. pallidicinctus_ 3L (bones not shown). × 2. L,M. Region surrounding obturator foramen of _T. pallidicinctus_ 3L, showing points of attachment of three parts of M. obturator (muscles removed). × 3. L. Lateral view. M. Medial view. N. Anterior view of left tarsometatarsus of _P. p. jamesi_ 4L, showing dorsal intrinsic muscles of foot. × 1-1/2. Tendon of M. extensor digitorum longus has been removed. 406 INTRODUCTION The purposes of this study were: (1) to obtain information on individual variation in the anatomy of the muscles and nerves of the leg of _Tympanuchus cupido pinnatus_ (Greater Prairie Chicken), _T. c. attwateri_ (Attwater's Prairie Chicken), _T. pallidicinctus_ (Lesser Prairie Chicken), and _Pedioecetes phasianellus jamesi_ (Sharp-tailed Grouse); (2) to determine whether or not the two species of the genus _Tympanuchus_ differ constantly in the myology of the leg; and (3) to determine what constant differences in the myology of the leg exist between the two closely related genera _Tympanuchus_ and _Pedioecetes_. These particular birds were chosen because they are closely related, and closely resemble one another in habitats occupied and in patterns of behavior. It was desired to study examples that showed as few adaptive differences as possible among the grouse. Series of each of the three species of grouse were readily obtainable, making it possible to draw comparisons at the level of individuals, subspecies, species, and genera. The study here reported on was begun in the spring of 1957 and was completed in the autumn of 1961. Prior work on the muscles of the leg of birds has been reviewed by Hudson (1937) and Hudson, _et al._ (1959). Only papers dealing with the innervation of the leg in birds are reviewed below.