Muscles of the Forearm Quiz

See Intermediate Layer. Option E is correct because flexor digitorum superficialis is the only muscle in the intermediate layer of the anterior forearm. The anterior (front) compartment of the forearm holds the flexors and pronators, arranged in three layers by depth: the superficial layer (flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres), the intermediate layer (flexor digitorum superficialis alone) and the deep layer (flexor digitorum profundus, flexor pollicis longus and pronator quadratus). Flexor digitorum superficialis has two heads, one from the medial epicondyle of the humerus and one from the radius, and it lies between the superficial and deep muscles. Some textbooks class it as superficial, but in the three-layer scheme it forms the middle layer. It splits into four tendons at the wrist that pass through the carpal tunnel and attach to the middle phalanx of each finger, so it flexes the proximal interphalangeal joints (the middle joints) and the metacarpophalangeal joints (the knuckles), and it also flexes the wrist. It is supplied by the median nerve. Memory aid: superficialis means more superficial than profundus (deep), but it still sits in the middle of the three layers.

• Intermediate layer: flexor digitorum superficialis is the only muscle in the intermediate layer of the anterior forearm.
• Other layers: the superficial layer holds flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres, and the deep layer holds flexor digitorum profundus, flexor pollicis longus and pronator quadratus.
• Action: it attaches to the middle phalanx of each finger and flexes the proximal interphalangeal joints.