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 diffe

Complete dissections of the muscles and nerves were made in eight legs (of five specimens) of the Lesser Prairie Chicken ( Tympanuchus pallidicinctus ), six legs (of four specimens) of the Greater Prairie Chicken ( T. cupido pinnatus ), three legs (of two specimens) of Attwater's Prairie Chicken ( T. cupido attwateri ), and six legs (of four specimens) of the Sharp-tailed Grouse ( Pedioecetes phasianellus jamesi ). For convenience and simplicity of reference, each specimen has been designated by

Skeleton The majority of the osteological terms used in the present paper are those used by Howard (1929); however, many skeletal features are not named by Howard. Since names for most of these parts were not found in the other literature examined, it was necessary for me to propose terms for them. Most of this new terminology pertains to the pelvis. All of the osteological terms used in the present paper, whether used by Howard or not, are briefly defined below. Those of the pelvis are illustra

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 K

Although no special study was made of the skeleton, certain conspicuous variations are discussed here. There are a few pronounced differences between the pelvis of Tympanuchus and that of Pedioecetes . Whereas in the former the thick lateral iliac process has a pronounced overhang with the ventral edge lateral to the ischium ( Fig. 1 ), in Pedioecetes there is no overhang at all and the edge of this process is much thinner. The ischium in Pedioecetes is wider (in dorsoventral extent), especially

For each nerve (or plexus) the condition found in most specimens of the Lesser Prairie Chicken ( T. pallidicinctus ) is described first. Following this, variations from the typical T. pallidicinctus condition are given for T. pallidicinctus , then for T. cupido (both subspecies considered together), and finally for P. p. jamesi . Lumbosacral Plexus , Figs. 2 , 3 T. pallidicinctus Description. —Eight spinal nerves contribute to the lumbosacral plexus. These are the second through the ninth synsac

In the accounts of the muscles the name used by Hudson, et al. (1959) for each muscle is given in parentheses after the name used by me if the two differ. In the account of each muscle, the description of the condition found in most specimens of the Lesser Prairie Chicken ( T. pallidicinctus ) is given first. This is hereafter referred to as the typical condition for T. pallidicinctus . Then any individual variations found within this species are given. Under the heading T. cupido any constant d

Analysis of Individual Variation Considerable individual variation occurs in both the muscles and the nerves of the leg of the three species studied. The amount of variation reported by a worker depends in large part on the degree of variation that he considers significant. Individual variation in the muscles and in the nerves will be discussed separately; that of the muscles (excluding innervation) will be considered first. Muscles Considering the number, rather than degree, of variations, the

The muscles and nerves were dissected in eight legs of the Lesser Prairie Chicken ( Tympanuchus pallidicinctus ), six legs of the Greater Prairie Chicken ( T. cupido pinnatus ), three legs of Attwater's Prairie Chicken ( T. c. attwateri ), and six legs of the Sharp-tailed Grouse ( Pedioecetes phasianellus jamesi ) for the purpose of obtaining information on individual variation as well as variation between these closely related species. Relatively little information is available regarding the ne