Meeting Abstract
Snakes use several locomotor behaviors as their speed and the terrain vary, and all but one of the major modes of terrestrial snake locomotion have known patterns of axial muscle activity that bend the body to generate propulsive forces. By contrast, as Lissmann described more than six decades ago, snakes can perform rectilinear locomotion with a straight body, and yet the underlying patterns of muscle activity have remained unknown. Hence, we obtained synchronized electromyograms and kinematics to test how the costocutaneous superior (CCS) and inferior (CCI) muscles and an intrinsic cutaneous muscle in between adjacent ventral scales (IV) of boa constrictors were used during this least understood mode of snake locomotion. The CCI muscles were active mainly during the propulsive phase when the ventral skin was maximally shortened and had static contact with the ground. Hence, CCI activity pulled the axial skeleton forward relative to both the ventral skin and the ground. The CCS activity during the recovery phase pulled the skin forward both relative to the axial skeleton and relative to the ground. The activity of the IV muscles began during the later stages of sliding contact with the ground and as the ventral skin shortened, and activity continued for almost the entire duration of static contact with the ground while the ventral skin remained maximally shortened. The snakes increased speed by increasing both the frequency and amplitude of movements as well as decreasing the portion of a locomotor cycle with static contact with the ground. With the exception of the activity of the IV during static contact with the ground when no shortening of the ventral skin occurred, our findings supported the long-standing and insightful hypotheses of Lissmann.
