How does the muscular sheath beneath a caecilian’s skin help it move?

Caecilians utilize a specialized axial musculoskeletal system to navigate their subterranean environment. The hypaxial muscles form an outer muscular sheath that is anchored to the skin by fibrous connective tissue.1

Because this sheath is largely disconnected from the underlying vertebral musculature, the skin and superficial muscles can move as a single, unified unit. This structural arrangement allows the caecilian to perform concertina locomotion, a process in which the body alternately folds and extends itself along its entire length. This movement can occur both through flexures of the entire body and within the envelope of the skin itself, providing the necessary leverage to tunnel through soil.12