Abstract
Because of its complexity, the facial musculature of rodents is potentially useful in systematics. Facial musculature of Aplodontia rufa is structurally rather simple and is similar to that of the Sciuridae, though most of the similarities are conditions or structures primitive for rodents in general. Aplodontia differs from sciurids in the loss of some components of the sphincter colli profundus and in reduction of the retroauricular muscles. Some of these differences can be correlated with adaptation for burrowing in Aplodontia. A large slip of trapezius is involved with the platysma in Aplodontia, a relationship interpreted as structural preadaptation for the formation of certain sorts of cheekpouch retractor muscles found in other rodents.