All six variations in the lumbosacral plexus were found on both sides of each specimen exhibiting the variation. In marked contrast to the other nerves, there was no significant variation in the lumbosacral plexus between the right and left sides of one individual. (This might not always be true, however, if a larger number of specimens were studied.) Of the variations in the lumbosacral plexus, one was found in only one specimen (of 15), one was found in three specimens, one in four specimens, two in six specimens, and one in seven specimens. Of the 34 variations found in the other nerves, 14 were found in only one leg (of 23), six occurred in two legs, four in three legs, three in four legs, three in five legs, two in six legs, one in seven legs, and one in nine legs.
Four of the variations were found only in specimens in which only one leg was dissected. Considering only those eight specimens in which both legs were dissected, and excluding the lumbosacral plexus, ten of the 30 variations were found in both legs of each specimen exhibiting the variation; 16 variations were found in only one leg of each specimen exhibiting the variation; four variations were found in both legs of some specimens but in only one leg of other specimens.
The number of variations in common between the two legs of one individual was compared with the number between individuals in the same manner as for the muscles; the lumbosacral plexus was excluded from consideration. See table 6. One leg of six of the eight specimens showed at least as many variations in common with a leg of another individual as with the other leg of the same individual. The two exceptions were T.p. 2L and T.p. 3R. Thus for most specimens there was as much variation in the nerves other than the lumbosacral plexus between the right and left legs of one individual as there was between individuals.
Of the 40 nerve variations (including the lumbosacral plexus) 11 were found only in T. pallidicinctus, seven were found only in T. cupido, and seven were found only in Pedioecetes. Four were found in both species of Tympanuchus (but not in Pedioecetes). Eleven were found in both Tympanuchus and Pedioecetes; of these, four were found in all three species, three were shared by T. pallidicinctus and Pedioecetes and four occurred in T. cupido and Pedioecetes.
The average number of variations per leg in both muscles and nerves was 11 in T. pallidicinctus, nine in T. cupido, and 16 in Pedioecetes. The high number in the last is in part the result of these being variations from the typical condition of T. pallidicinctus (rather than from Pedioecetes).
Analysis of Variation Between Species
No constant differences in the muscles or nerves was found between T. cupido pinnatus and T. cupido attwateri. Only one constant difference was found between T. cupido and T. pallidicinctus: a thicker fleshy origin of M. extensor iliotibialis lateralis in T. cupido (associated with a thicker edge of the lateral iliac process).
Although no constant differences in the nerves were found between Pedioecetes and Tympanuchus (both species), 17 constant differences in the muscles were found between these two genera. Seven of these differences pertain to features of a single muscle—M. flexor cruris medialis. Compared with the condition in Tympanuchus, M. flexor cruris medialis in Pedioecetes has a wider origin, a partly fleshy (instead of entirely tendinous) origin, a more pronounced curvature of the line of origin, a wider insertion, an insertion posterior (rather than anterior) to the medial collateral ligament, an insertion that attaches in part to the articular capsule, and a shorter tendon of insertion (resulting in the fusion of the common insertional tendon of Mm. flexor cruris lateralis and femorocruralis with the fleshy belly rather than with the insertional tendon). Other differences include the following. A more extensive posteroproximal aponeurosis of M. extensor iliotibialis lateralis in Pedioecetes (resulting in a narrower fleshy origin); a more nearly straight line of origin of this muscle (associated with a less pronounced lateral iliac process); a thinner fleshy origin of this muscle (associated with a thinner edge of the lateral iliac process); a wider M. flexor cruris lateralis that is fleshy up to the origin from the vertebrae; a wider fleshy origin of M. iliacus; the origin of M. caudofemoralis pars iliofemoralis not reaching the ventral edge of the ischium; a narrower origin of M. adductor superficialis; a wider M. femorocruralis; and a shorter belly of M. extensor digitorum longus. Some additional differences between these two genera, which are slight in degree, are given in the accounts of the muscles. If additional specimens were studied, some of the differences listed above possibly would prove to be subject to individual variation and so could not properly be listed as constant differences between the two genera.
The picture of the differences between Tympanuchus and Pedioecetes that the present study presents is radically different from that presented by the study of Hudson, et al. (1959). These authors reported the following differences between these two genera. (I am using my terminology.) The origin of M. piriformis is narrower in Pedioecetes and is more posteriorly situated; the belly of M. extensor iliotibialis anticus is broader in Pedioecetes; the belly of M. tibialis anticus is longer; the belly of M. peroneus brevis is shorter; the insertional tendon of the anterolateral head of M. flexor perforatus digiti III is shorter; the belly of M. flexor digitorum longus is shorter; only two (rather than three) of the branches of M. extensor digitorum longus on the tarsometatarsus are ossified; the posterior metatarsal crest is shorter; M. flexor perforans et perforatus digiti II has two heads in Pedioecetes but only one in Tympanuchus; the roof over the hypotarsal canal enclosing the tendon of M. flexor digitorum longus is bony in Pedioecetes but fibrous in Tympanuchus; M. flexor cruris lateralis is wider in Pedioecetes; and the origin of M. femorocruralis is wider. I paid particular attention in my study to these 13 features given by Hudson, et al.; of these the only differences that I found to be constant were the last two. The apparent reason for this great discrepancy is the small number of legs of Tympanuchus studied by Hudson, et al. They studied eight legs of Pedioecetes but only two legs of Tympanuchus. This emphasizes the danger of making comparisons based on a very small number of specimens (a criticism which may prove to apply to the present study as well). The reason why Hudson, et al. did not report most of the differences found by me is not so apparent. Either the specimens studied by the former workers showed a greater variation in these characters than did my specimens or else those workers overlooked the differences. Probably both factors are involved. It remains to be determined how many specimens need to be studied in order to obtain a fairly accurate picture of variation.
Comparison with Other Studies of Innervation