Morphological study of nerve endings in jaw muscles of post-hatching American alligators (Alligator mississippiensis).

Two months after hatching, the fibers of the jaw muscles of the American alligator are associated with three types of nerve terminals namely, plates, simple plates, and grape endings. Simple plate endings are mainly observed on the small muscle fibers. Grape-type endings are found on muscle fibers that resemble the tonic fibers of garter snakes (Hess, Am. J. Anat., '63). Most terminals are plate endings and account for 53.7-74.7% of terminals per muscle. Fibers with grape-type endings were found in all the jaw muscles studied; they lack well organized T-systems, M-lines, and post-junctional sarcolemmal folds, as well as irregularly distributed small of fibrils, and zigzag Z-lines. The properties of nerve endings of the American alligator indicate that M. depressor mandibulae, M. pseudotemporalis, and M. pterygoideus posterior have primary roles in jaw movements. M. pterygoideus anterior and M. intramandibularis contribute mainly to postural adjustments of the jaws. The multiplicity of nerve terminals in the jaw muscles of American alligators contrasts with the simple movements of their jaws. © 1994 Wiley-Liss, Inc.