The malleoli form prominent landmarks, the tip of the external malleolus being about ½ inch below and behind that of the internal, while, owing to the greater breadth of the latter, their posterior borders are on a level with one another. In front of the external malleolus and external to the tendon of the peroneus tertius, -and between the internal malleolus and tendon of the tibialis anticus, are shallow depressions, which denote the position of the ankle-joint. These depressions are replaced by swellings, when the joint becomes distended. The joint line lies about ½ inch above the tip of the internal malleolus. Less than 1 inch below and in front of the external malleolus lies the peroneal spine of the os calcis, with the peroneus brevis above and the peroneus longus below it, while less than 1 inch below the internal malleolus is the sustentaculum tali of the os calcis, into which the recurrent slip of the tibialis posticus is inserted, while the flexor longus digitorum and flexor longus hallucis occupy the underlying groove. The tubercle of the scaphoid, which receives the chief insertion of the tibialis posticus, lies about 1 inch in front of the internal malleolus ; and over 2 inches in front of the external malleolus is the projecting base of the fifth metatarsal, with the cuboid behind it. The mid-tarsal joint, that between calcaneum and cuboid and between the astragalus and scaphoid, lies internally just behind the tubercle of the scaphoid, and externally just in front of the midpoint between the external malleolus and the base of the fifth metatarsal. When the foot is extended, the astragalus forms a prominence most marked in front of the external malleolus, and below, in front, and a little to the outside of this prominence is a depression, which lodges the outer end of the astragalo-calcaneal ligament, and still farther in front is a slight prominence, due to the anterior tuberosity of the os calcis, which articulates with the cuboid in front The tendons lying in front of the ankle are best seen when the foot is extended, and consist from within outwards of tibialis anticus, extensor longus hallucis, extensor longus digitorum, and peroneus tertius, while on the outer aspect of the dorsum the belly of the extensor brevis digitorum can be felt.
The sole of the foot presents a triangular outline, and only a comparatively small portion of it comes normally in contact with the ground. The parts which touch the ground are the heel, external border of the foot, and ball of the great toe. The foot is arched antero-posteriorly, arid also transversely.
The antero-posterior arch is formed by bony pillars-os calcis and astragalus posteriorly, and the anterior tarsus and metatarsus anteriorly-and is maintained by the plantar fascia, the plantar and inferior calcaneo-scaphoid ligaments, .and tendons of the peronei, tibiales, flexores longus digitorum and hallucis.
The transverse arch is formed by the wedge shape of the middle and external cuneiform bones, and second, third, and fourth metatarsals, and is supported by the peroneus longus tendon and short ligaments of the part. In the front of the foot the whole of the first metatarsal and its sesamoid bones can be fairly made out. It articulates behind with the internal cuneiform. The metatarso-phalangeal articulations are about 1 inch behind the webs of the toes. Posteriorly the tendo Achillis forms a prominent landmark. The depression to its outer side lodges the tendons of the peronei longus and brevis, the latter lying anteriorly and more deeply, in contact with the fìbula, while that on its inner side is continuous with the groove under the sustentaculum tali, in which are lodged the tibialis posticus (next the tibia), then the flexor longus hallucis, the posterior tibial artery and venae comités, posterior tibial nerve and flexor longus pollicis. As these latter tendons, with the vessels and nerve, lie well in front of the tendo Achillis, they run little risk of being wounded in a tenotomy of the latter. A bursa separates the lower portion of the tendo Achillis from the os calcis, and when inflamed this bursa may cause swelling and pain suggestive of an affection of the ankle-joint, and may even lead to disease of the os calcis. Tenotomy of the tendo Achillis is performed by introducing a blunt-pointed tenotome between the skin and the tendon through a puncture made in the skin, while the foot is kept extended so as to relax the tendon. Then the edge of the tenotome having been turned against the tendon, the foot is forcibly flexed, thereby rendering the tendon tense, and dividing it against the blade, a considerable gap existing subsequently.
The dorsalis pedis artery runs from the middle of the ankle-joint to the space between the bases of the first two metatarsals lying to the outer side of the extensor longus hallucis tendon. Starting from a point midway between the tip of the internal malleolus and the heel, the plantar arteries run- the internal to the middle of the under surface of the great toe, the external to a point about 1 inch from the base of the fifth metatarsal, whence it turns inwards.
The skin over the ankle and dorsum of the foot is thin and freely movable, and is readily damaged from pressure on the subjacent parts. On the sole of the foot the parts which come in contact with the ground are thick and fairly adherent to the dense subcutaneous tissue, while the remainder of the skin of the sole is thin, smooth, and sensitive, and well supplied with sweat-glands. In some respects the skin and subcutaneous tissue of the sole resembles that of the palm ; it does not tend to retract when cut ; and foreign bodies, such as broken needles, when embedded in it, are frequently difficult to find, while abscesses remain localized, and cause much pain.
The subcutaneous tissue is lax over the ankle and dorsum, and is frequently the part first affected in dropsy ; is abundant and fatty around the tendo Achillis, and thick, dense, and fibrous over the heel (where it may be ¾ inch thick), and over the parts which come in contact with the ground. This thick pad forms an excellent cushion, and, combined with the elasticity of the arches of the foot, prevents jarring in walking.