In human anatomy, the flexor digitorum profundus is a muscle in the forearm that flexes the fingers. It is considered to be an extrinsic muscle because its action is at a different location than the main body of the muscle.

Flexor digitorum profundus, along with flexor digitorum superficialis have long tendons that run down the arm and through the carpal tunnel and attach to the palmar side of the phalanges of the fingers. This muscle originates from the anterior side of the ulna.

Flexor digitorum profundus lies deep to superficialis, but it attaches more distally. To get around this problem profundus's tendons go through the tendons of superficialis, and end up attaching to the distal phalanx.

Innervation

Flexor digitorum profundus is innervated by the median and ulnar nerves.

• The medial aspect of the muscle (which flexes the 4th and 5th digit) is supplied by the ulnar nerve (C8, T1)
• The lateral aspect (which flexes the 2nd and 3rd digit) by the median nerve (via its anterior interosseous branch) (C8, T1).

It is one of two flexor muscles that is not exclusively supplied by the median nerve (the other is flexor carpi ulnaris).

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