A flexor muscle.
Flexor
The flex
The flexor is a muscle that bends part of your body.
Extender
A muscle that is an elevator raises or lifts a part.
The muscle in the thigh is called a quadriceps. It is a body part.
knee
An extensor straightens part of your body.
A muscle called the Diaphragm
quadricep
A muscle which bends or flexes any part; as, the flexors of the arm or the hand; -- opposed to extensor.
the ciliary muscle is the smooth muscle of the ciliary body