The foot is acted upon by long muscles which come down from the leg and short muscles which arise in the foot itself. Of these the long muscles are the more important because they influence the position of the foot itself, whereas the short muscles act on the toes; as stated the movements of the toes are of secondary importance (page 562). The functions of the muscles are active or dynamic in character. They bear the weight of the body when in motion and direct the movements of the foot in locomotion. Their function and structure are to be studied together, as one explains the other, and a knowledge of them explains many deformities and indicates their treatment.

The long muscles have three distinct actions on the foot: (1) they support the arch of the foot; (2) they flex and extend the foot; (3) they abduct and adduct the foot - this latter being associated with a certain amount of rotation.

The action of the individual muscles is not a simple one. They act on two joints, the ankle and subastragaloid. If the former is stationary they abduct and adduct, if the latter is stationary they flex and extend, but if both move then a combined action of the muscles is necessary.

For our purposes we may divide the muscles into four groups of three each (page 546). They are (1) extensors, (2) flexors, (3) abductors, (4) muscles of the calf.

1. Extensor group: tibialis anterior, extensor longus hallucis, extensor longus digitorum.

2. Flexor group: tibialis posterior, flexor longus digitorum, flexor longus hallucis.

3. Abductor group: peroneus longus, peronetis brevis, perofieus tertius.

4. Muscles of the calf: gastrocnemius, soleus, piantaris.