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The posterior compartment of the forearm (or extensor compartment) contains twelve muscles which primarily extend the wrist and digits. [2] It is separated from the anterior compartment by the interosseous membrane between the radius and ulna .
Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extending the flexed (bent) elbow. Straightening of the arm would require extension at the elbow joint. If the head is tilted all the way back, the neck is said to be extended.
The extensor digitorum muscle (also known as extensor digitorum communis) [2] is a muscle of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand. Extensor digitorum is innervated by the posterior interosseous nerve, which is a branch of the radial nerve. [3]
The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. Extrinsic denotes their location outside the hand. Extensor denotes their action which is to extend, or open flat, joints in the hand.
The extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint. The muscle is a minor extensor of the carpus in carnivores, but has become a flexor in ungulates. In this case it would be described as ulnaris lateralis.
Split tendons of the muscle inserting on both ulnar and the radial side of the common extensor digitorum was also reported. [2] Anomalous hand extensors including the extensor medii proprius and the extensor indicis et medii communis are often seen as variations of the extensor indicis [2] due to the shared characteristics and embryonic origin. [8]
The common extensor tendon serves as the upper attachment (in part) for the superficial muscles that are located on the posterior aspect of the forearm: Extensor carpi radialis brevis; Extensor digitorum; Extensor digiti minimi; Extensor carpi ulnaris [1] [2]
Deep muscles of the chest, including pectoralis minor, serratus anterior, and subclavius (Gray 1918) Pectoralis major is a thick, fan-shaped or triangular convergent muscle, which makes up the bulk of the chest muscle. It lies under the breast. It serves to flex, extend, and rotate the humerus, the long bone of the upper arm.