Muscles of the foot, historical artwork. The figure at top left shows the first layer of muscles (red) in the sole of the foot. The skin and fascia (connective tissue) have been removed. At top right is the second layer, and at bottom right is the third and deepest layer of muscles in the sole of the foot. The underside of the heel bone (os calcis) is at top. Flexor and abductor muscles that move the toes attach to the heel bone. The figure at bottom left shows the muscles on the upper surface of the foot, which include the extensor muscles of the toes. Published in The Muscles of the Human Body... by Jones Quain in 1836.