Biceps and triceps muscles in the upper arm. Left: biceps contracted. Right: triceps contracted
Either of two muscles that are split in two in their upper part to form a Y-shape. Biceps brachii is the chief upper arm muscle; it runs along the humerus – the large bone of the upper arm – and is connected to the radius at one end and the scapula, or shoulder-blade, at the other. Contraction of the biceps causes the arm to flex at the elbow joint. It works antagonistically with the triceps, which contracts to extend the arm. Biceps femoris is a thigh muscle, attached to the pelvis, the femur, and the fibula.
