Muscles of the forearm, historical artwork. The figure at left shows the first layer of muscles (red) on the back of the forearm and hand. The skin and fascia (connective tissue) have been removed to expose the musculature and tendons. At right is the second layer of muscles after the first have been removed. The muscles of the lower arm are used to operate the wrist and hand. The muscles attach to the ulna and radius bones, and to the humerus of the upper arm. The extensor tendons of the fingers are kept in place by the annular ligament of the wrist (strap-like, lower left). Published in The Muscles of the Human Body... by Jones Quain in 1836.