There are many muscles in the forearm, this is due to the great complexity and variety of hand movements. They are distributed in three regions (frontal, lateral and posterior) and most of them have a thin muscular belly and an elongated tendon which reaches the hand running between the bone plane and the transverse and dorsal carpal ligaments.
The muscles of the anterior region are eight and are arranged on four layers: • first layer: includes the four epitrochlear muscles, which from lateral to medial are the Pronator Teres muscle, Flexor Carpi Radialis, Palmaris Longus and Flexor Carpi Ulnaris and which have a common tendon at their origin on the epitrochlea (the medial condyle of the humerus); • second layer: is formed by the Flexor Digitorum Superficialis – Hand; • third layer: it includes the Flexor Digitorum Profundus – Hand and the Flexor Pollicis Longus; • fourth layer: is composed by the Pronator Quadratus muscle.
The muscles of the lateral region are arranged on two layers: • superficial layer, which includes the Brachioradialis, Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis; • deep layer: the Supinator muscle.
The muscles of the posterior region are eight and are arranged on two layers: • superficial layer: which includes the four epicondylar muscles (Extensor Digitorum, Extensor Digiti Minimi, Extensor Carpi Ulnaris and Anconeus) that have a common tendon at their origin on the lateral epicondyle; • deep layer: is composed by the Abductor Pollicis Longus, Extensor Pollicis Brevis, Extensor Pollicis Longus and Extensor Indicis.
The muscles of the anterior region are eight and are arranged on four layers: • first layer: includes the four epitrochlear muscles, which from lateral to medial are the Pronator Teres muscle, Flexor Carpi Radialis, Palmaris Longus and Flexor Carpi Ulnaris and which have a common tendon at their origin on the epitrochlea (the medial condyle of the humerus); • second layer: is formed by the Flexor Digitorum Superficialis – Hand; • third layer: it includes the Flexor Digitorum Profundus – Hand and the Flexor Pollicis Longus; • fourth layer: is composed by the Pronator Quadratus muscle.
The muscles of the lateral region are arranged on two layers: • superficial layer, which includes the Brachioradialis, Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis; • deep layer: the Supinator muscle.
The muscles of the posterior region are eight and are arranged on two layers: • superficial layer: which includes the four epicondylar muscles (Extensor Digitorum, Extensor Digiti Minimi, Extensor Carpi Ulnaris and Anconeus) that have a common tendon at their origin on the lateral epicondyle; • deep layer: is composed by the Abductor Pollicis Longus, Extensor Pollicis Brevis, Extensor Pollicis Longus and Extensor Indicis.