Final answer:
The posterior compartment of the forearm has twelve muscles divided between two layers: the superficial and deep layers, with the superficial layer contributing to wrist and finger extension and the deep layer facilitating thumb and finger movements.
Step-by-step explanation:
The posterior compartment of the forearm contains a total of twelve muscles, which are distributed between two distinct layers: a superficial layer and a deep layer. The superficial layer includes muscles such as the extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and the extensor carpi ulnaris. These muscles originate on the humerus and are primarily involved in the extension of the wrist and fingers. The deep layer of the posterior compartment comprises muscles that originate on the radius and ulna, including the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. These muscles facilitate the movement of the thumb and fingers, such as abduction and extension.
The posterior compartment of the forearm consists of a total of five muscles distributed between two layers. In the superficial posterior compartment, which originates on the humerus, there are the extensor radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. In the deep posterior compartment, which originates on the radius and ulna, there are the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis, and their associated blood vessels and nerves.