Foot. 1. The bones of the foot may be divided into three groups - viz. Tarsus, Metatarsus, and Phalanges. The bones of the tarsus are seven in number - viz. the astragalus, os calcis, cuboid, scaphoid, and the three cuneiform bones (internal, middle, and external). The astragalus articulates with the tibia above, entering into the formation of the ankle joint; it rests upon the os calcis below, and articulates with the scaphoid in front. The os calcis forms the bony prominence of the heel. The cuboid is situated in front of the os calcis on the outer side of the foot, and articulates anteriorly with the fourth and fifth metatarsal bones, and internally with the external cuneiform bone. In front of the scaphoid on the inner side of the foot is the internal cuneiform bone; just external to it is the middle, and outside this again is the external cuneiform bone. In front of the tarsus is the metatarsus, consisting of five bones: the three internal metatarsal bones articulating with the cuneiform bones, and the two external metatarsal bones articulating as aforesaid with the cuboid. Anteriorly to the metatarsal bones are the phalanges, numbering fourteen bones in all, two for the great toe and three for each of the other toes. The bones of the foot are united one to another by strong ligaments, and these ligaments, together with the tendons of muscles which are attached to the bones, serve to maintain the shape of the foot. An examination of an antero-posterior section of a foot shows that the weight of the body, transmitted through the astragalus, is borne by ah arch, the hinder portion of which is formed by the os calcis, while the front portion terminates in the balls of the toes. This arch is called the plantar arch. The weakest point in the mechanism of this arch is found to be just below the anterior portion or head of the astragalus. This portion of bone rests upon a ligament which unites the scaphoid with the os calcis, and is further strengthened by the tendon of the posterior tibial muscle (a muscle which winds round the os calcis and passes forward to be inserted into the scaphoid). If the arch gives at all at this point the condition known as flat-foot results. The groups of muscles which act upon the foot may be briefly alluded to. The calf muscles act through their tendon (the tendo Achillis) upon the prominence of the os calcis, and when they contract the heel is raised and the toes are brought more or less into line with the lower leg. The muscles which are situated in front of the lower leg, acting through their tendons, elevate, on the other hand, the front of the foot. Thus flexion and extension at the ankle joint are effected, the former being brought about by the nrascles of the front of the leg, the latter by the calf muscles. The peronei muscles rotate the foot outwards (abduction), while the tibialis anticus and tibialis posticus rotate it inwards (adduction). The toes are flexed by muscles and tendons running through the sole of the foot, and extended by muscles coursing over the back or dorsum of the foot. It so happens, then, that flexion at the ankle joint and extension of the toes are associated actions, in part brought about by identical muscles situated in the front of the leg, and running over the dorsum of the foot; while similarly extension at the ankle joint and flexion of the toes are effected by muscles situated at the back of the leg and lying beneath (i.e. in the sole of) the foot. Beneath the skin of the sole, which is thick and resistant, is a padding of fat, and underneath this again is a strong fascia, the plantar fascia.
2. The foot is the ordinary English unit of length. It is one-third of the standard yard, and was taken originally from the length of the human foot. Similarly the French have a unit they call the pied usuel, which is a third of the standard metre. This is distinct from the Paris foot, which is about one per cent. smaller. The English foot is divided into 12 inches, and each of these into 12 lines.
Paris foot = 12-78012 English inches.' Rhenish foot = 12-35t>52 .