The two points of attachment of each muscle are its origin and insertion. At these attachment points, the muscle is connected to the bone by a tendon. Some broad, sheetlike tendons are called aponeuroses. A retinaculum is a band of connective tissue that holds down the tendons at each wrist and ankle. The origin, also called the head, is the most stationary end of the muscle. The insertion is the end of the muscle attached to the bone undergoing the greatest movement. Origins are usually, but not always, proximal or medial to the insertion of a given muscle. The part of the muscle between the origin and the insertion is the belly. Some muscles, such as the biceps brachii with two heads and the triceps brachii with three heads, have multiple origins, or heads.