Final answer:
The muscle not located entirely within the hand is the Flexor carpi radials, which is an extrinsic muscle that originates in the forearm and assists in flexing the wrist.
Step-by-step explanation:
All of the following muscles are located entirely within the hand except for one, which is the Flexor carpi radialis. The muscles located within the hand are the intrinsic muscles, and they include the thenar, hypothenar, and intermediate muscle groups like the lumbricals and interossei. The Flexor carpi radialis is an extrinsic muscle, meaning it originates in the forearm and inserts into the hand, and is responsible for flexing and abducting the wrist. On the other hand, the Flexor digitorum superficialis and Flexor digitorum profundus muscles are involved in flexing the fingers and the hand at the wrist, while the Flexor pollicis longus muscle is involved in flexing the thumb.