tubulus transversus

tu·bu·lus trans·ver'·sus

a tubular invagination of the sarcolemma of skeletal or cardiac muscle fibers that surrounds myofibrils as the intermediate element of the triad in skeletal muscle and the diad in cardiac muscle; involved in transmitting the action potential from the sarcolemma to the interior of the myofibril.
Synonym(s): T tubule