#anatomy #forearm #muscles
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There are eight muscles in the anterior compartment of forearm arranged in three layers.
The superficial layer contains four of these muscles, all of them having a common origin from the front of medial epicondyle of humerus.
First muscle to be indicated, and the most lateral one is the pronator teres. This muscle actually have two heads of origin; the superficial head originates from the medial epicondyle of humerus and its deep head originates from the medial margin of coronoid process of ulna. Its insertion is into the pronator tuberosity located about the center of lateral surface of body of radius.
The next muscle is flexor carpi radialis. Its origin is from the medial epicondyle of humerus and its insertion is on the bases of the second and third metacarpal bones.
The Palmaris longus muscles is a slender muscle which may be absent. Then present this muscle originates from the medial epicondyle of humerus and its insertion is into the palmar aponeurois.
The last muscle to be indicated and the most medial one of the superficial layer is the flexor carpi ulnaris. This muscle originates from the medial epicondyle of humerus but also from the medial margin of olecranon. Its tendon inserts directly into the pisiform bone and indirectly into the base of fifth metacarpal bone by way of pisometacarpal ligament and into the hook of hamate by way of pisohamate ligament.
On the next diagram we will indicate the intermediate layer of anterior compartment of forearm. This layer contains only one muscle, the flexor digitorum superficialis.
This muscle have two origins. The humero-ulnar origin is from the medial epicondyle of humerus, ulnar collateral ligament and medial margin of coronoid process of ulna. The radial origin is from the anterior oblique line of radius. A tendinous arch is joining its two origins.
The flexor digitorum profundus inserts by way of four tendons into the middle phalanges of the last four fingers. Before insertion each of the four tendons splits into medial and lateral slips, which are inserted into the corresponding sides of the middle phalanx.
An important mention is that bellow the tendinous arch of flexor digitorum superifialis are passing the median nerve and the ulnar artery.
On the last diagram we will draw the deep layer of the anterior compartment of forearm. This layer contains three muscles.
Originating from the upper two thirds of the anterior surface of radius bellow the oplique line and from the adjacent medial half of the interosseous membrane is the flexor policis longus. Its tendon inserts into the base of distal phalax of thumb.
Having origin from the upper three fourths of the anterior and medial surfaces of the body of ulna and the adjoining part of interosseous membrane is the flexor digitorum profundus. This muscle inserts by way of four tendons into the bases of distal phalanges of the last four fingers.
The last muscle to be indiated is the pronator quadratus. It is a flat quadrilateral muscle, which extends across the front of the distal parts of the radius and ulna, thus being placed behind the tendons of flexor policis longus and flexor digitorum profundus. Its origin is from the lower ¼ of the anterior surface of ulna. Its insertion is into the lower ¼ of anterior surface of radius.
Regarding the innervation of the muscles of the anterior compartment of forearm keep in mind that all the muscles are innervated by the median nerve with two exceptions. The flexor carpi ulnaris which is supplied by the ulnar nerve and the medial half of the flexor digitorum profundus which is also supplied by the ulnar nerve.

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