On the form and function of the abductor pollicis brevis muscle.

The abductor pollicis brevis muscle acts in conjunction with the palmaris longus and the abductor pollicis longus to abduct the first metacarpal in the sagittal plane. Segments of the abductor pollicis brevis which arise from the tendons of the palmaris longus and/or the abductor pollicis longus and are inserted into the extensor expansion are the lumbricals of the thumb. The lateral border of the abductor pollicis brevis presents an important muscular (in four cases out of ten neurovascular) hilum. The tendinous slip to the abductor pollicis brevis from the palmaris longus presents near its origin an orifice which the palmar branch of the median nerve traverses to become superficial.