Variations of the cephalic muscles in the colubrid snake genera Entechinus, Opheodrys, and Symphimus

The cephalic muscles in three species of Entechinus, two species of Opheodrys, and Symphimus mayae display patterns of interspecific variation that are largely congruent with patterns of variation previously described for the skulls of these species. This congruence does not stem from direct correlation between the shapes of associated bones and muscles. In these colubrid snakes, most interspecific variations in muscle form involve changes in the shape or relative position of attachment points that appear unrelated to changes in the gross form of the bony surfaces forming the attachment points and produce no major changes in the architectural array of fibers in the muscle. Data presented here, combined with information from previous comparative studies of colubroid cephalic muscles, support the hypothesis that these muscles are limited in their potential variability by factors favoring parallel arrangements of fibers.