Flexor muscle of Arm region muscles are situated around the posterior and medial aspects of the forearm. They are arranged in two layers – superficial and deep.
- Superficial layer
- Pronator teres
- Flexor carpi radialis (Medial flexor of the carpus)
- Flexor carpi ulnaris (Middle flexor of the carpus)
- Ulnaris lateralis (Flexor metacarpi externus)
- Deep layer
- Superficial digital flexor (Flexor pedis perforatus)
- Deep digital flexor (Flexor pedis perforans)
FLEXOR MUSCLES – SUPERFICIAL LAYER
Pronator teres
- It is a very small, feeble and vestigeal muscle situated along the medial face of the elbow joint, closely blended with the medial lateral ligament.
- Origin: Medial epicondyle of the humerus.
- Insertion: Upper part of the medial border of the radius.
- Action: Inappreciable as it is vestigeal.
- Blood supply: Median artery.
- Nerve supply: Median nerve.
Flexor carpi radialis (Medial flexor of the carpus)
- This is a narrow muscle placed immediately behind the preceding.
- Origin: Medial epicondyle of the humerus. The tendon is provided with a synovial sheath above the carpus.
- Insertion: A tubercle on the postero-medial part of the upper extremity of the large metacarpal bone.
- Action: To flex the carpus and extend the elbow.
- Blood supply: Median artery.
- Nerve supply: Median nerve
Flexor carpi ulnaris (Middle flexor of the carpus)
- This is a wide muscle situated behind the preceding and covers the medial surface of the forearm.
- Origin: Has two heads of origin – humeral head from the medial epicondyle of the humerus and ulnarhead from the medial face of the olecranon.
- Insertion: The supero-medial half of the accessory carpal bone.
- Action: To flex the carpus and extend the elbow.
- Blood supply: Median artery.
- Nerve supply: Ulnar nerve.
Ulnaris lateralis (Flexor metacarpi externus)
- It is a large, thick muscle situated behind the lateral digital extensor.
- Origin: Lateral epicondyle of the humerus.
- Insertion: By a short thick tendon to the supero-lateral half to the carpal bone and by a narrow long tendon to the lateral aspect of the upper extremity of the large metacarpal.
- Action: To flex the carpus and extend the elbow.
- Blood supply: Collateral radial artery.
- Nerve supply: Radial nerve.
FLEXOR MUSCLES – DEEP LAYER
Superficial digital flexor (Flexor pedis perforatus)
- This muscle is under cover of flexor carpi ulnaris.
- Origin: Medial epicondyle of humerus.
- Its muscular belly divides into two parts at the lower third of the forearm. Each end terminates in a tendon and the superficial one passes over the carpal canal. It is provided with a synovial sheath below the level of the accessory carpal. The deep part passes through the carpal canal in company with the deep flexor and is connected to it by a strong fibrous band. The common tendon divides above the fetlock into branches each of which forms along with a branch of the posterior division of the suspensory ligament, a ringfor the passage of the tendon of the deep flexor of the digit. The tendon of the deep part has a synovial sheath in the carpal canal. The ring, through which the deep flexor passes, is provided with a synovial sheath.
- Insertion: The volar face of the upper extremity of the second phalanges.
- Action: To flex the digits and carpus and extend the elbow.
- Blood supply: Median artery.
- Nerve supply: Ulnar and median nerves.
Deep digital flexor (Flexor pedis perforans)
- This is the largest of the flexor muscles and is partly under the cover of the preceding.
- Origin: It has three heads of origin – humeral, radial and ulnar.
- The humeral heads are two, and arise from the medial epicondyle of the humerus.
- The radial head is the deepest and smallest and arises from the lateral part of the volar face of the radius at its upper half.
- The ulnar head is the most superficial and is situated between the flexor carpi ulnaris and ulnaris lateralis. It arises from both the faces of the olecranon.
- Each head is succeeded by a tendon, which unite and form a common tendon just above the carpus. The common tendon passes through the carpal canal and in metacarpal region it passes between the suspensory ligament in front and the superficial digital flexor tendon behind. It divides above the fetlock into two divisions, which pass through the ringsof the superficial flexor. The tendon of the muscle is provided with synovial sheaths in the carpal canal and the rings formed by the superficial flexor in the fetlock.
- Insertion: The volar surfaces of the third phalanges of the two digits.
- Action: To flex carpus and digits and extend elbow.
- Blood supply: Median artery and common interosseous artery.
- Nerve supply: Median and ulnar nerves.
- The lumbricales of the horse are absent, unless we regard as such the muscle bundles which arise on the deep flexor and are inserted into the superficial flexor tendon at the carpus.
- The interossei musculi is only one – interosseous medius or suspensory ligament is present.
