The mechanics of swallowing and the muscular control of diverse behavioursin gopher snakes

Snakes are excellent subjects for studying functional versatility and poten tial constraints because their movements are constrained to vertebral bendi ng and twisting. In many snakes, swallowing is a kind of inside-out locomot ion. During swallowing, vertebral bends push food from the jaws along a sub stantial length of the body to the stomach. In gopher snakes (Pituophis mel anoleucus) and king snakes (Lampropeltis getula), swallowing often begins w ith Lateral bending of the head and neck as the jaws advance unilaterally o ver the prey. Axial movement then shifts to accordion-like, concertina bend ing as the prey enters the oesophagus. Once the prey is completely engulfed , concertina bending shifts to undulatory bending that pushes the prey to t he stomach. The shift from concertina to undulatory bending reflects a shif t from pulling the prey into the throat (or advancing the mouth over the pr ey) to pushing it along the oesophagus towards the stomach. Undulatory kine matics and muscular activity patterns are similar in swallowing and undulat ory locomotion, However, the distinct mechanical demands of internal versus external force exertion result in different duty factors of muscle activit y. Feeding and Locomotor movements are thus integral functions of the snake axial system.