THE TARSAL BONES. 419 



THE FOOT. 



The framework of the foot consists of the tarsus, metatarsus, 2XiA phalanges, 

 which differ in their proportionate size from the corresponding divisions of the hand. 

 Thus, in the latter the carpal region is the shortest and that of the phalanges the 

 longest, equalling almost precisely the other two ; in the foot, on the contrary, the 

 region of the phalanges is the shortest and that of the tarsus makes about half the 

 entire length. The tarsus differs also in its arrangement more than the carpus from 

 the primitive type. The tarsal bones may be considered as divided into two lateral 

 divisions : an outer series of two bones bearing the two outer toes, and an inner 

 series of five bearing the three inner toes, so placed that the proximal bone of the 

 inner part rests on top of the proximal of the outer. The outer side of the skeleton 

 of the foot rises but little from the ground, while the inner is highly arched. 



THE TARSAL BONES. 



The tarsal bones are the calcanenm, or os calcis, the heel-bone ; the cuboid, which 

 with it forms the outer division ; the astragalus, or talus, which joins the leg ; the 

 scaphoid, placed between the astragalus and the three cuneiform, which bear the 

 three inner metatarsals. 



THE CALCANEUM. 



The calcaneum ^ is a narrow elongated bone forming the heel, supporting the 

 astragalus, and joining the cuboid in front. It has six surfaces. The inferior sur- 

 face presents at the back a swelling subdivided into the interiial and external playi- 

 iar tubercles, of which the former is much the larger, forming the posterior pier of 

 the foot. These tubercles are continuous at the posterior border, in front of which 

 a deep notch divides them. Each appears on its side of the bone. In front of 

 these the lower surface, convex from side to side, is marked by longitudinal grooves. 

 Near the front is the anterior tubercle, a small swelling, from which and from a 

 depression near it arise calcaneo-cuboid ligaments. The posterior surface is 

 roughly oval with the small end up. The ten do Achillis is attached to a roughness 

 occupying its lower half, above which the bone slants forward and is smooth for a 

 bursa between it and the tendon. The lower part of the posterior surface is con- 

 tinuous with the plantar tubercles. The internal surface is smooth and concave ; 

 for the internal tubercle projects strongly inward, while in front and above there is 

 a shelf-like process, the siistentaculum tali, to support the head of the astragalus, 

 slanting downward and forward. Beneath this is a slight groove for the tendon of 

 the long flexor of the great toe. Lower down near the front border a depression 

 for a ligament to the cuboid runs down in front of the anterior tubercle. The ex- 

 ternal surface is the longest. It presents about its middle a vague tubercle for 

 the middle bundle of the outer lateral ligament of the ankle, and nearer the front 

 a larger one, \h.Q. peroneal spine. When well marked this is a ridge, covered with 

 cartilage, slanting downward and forward, separating two grooves for the tendons of 

 the peroneus longus and 'brevis. The outer posterior plantar tubercle projects 

 somewhat on this side. Rather more than the anterior two-thirds of the superior 

 surface are devoted chiefly to the joints with the astragalus ; the posterior portion 

 is convex from side to side and concave from before backward. There are two 

 articular facets : X\\& posterior facet, the larger, a vaguely four-sided swelling, occu- 

 pies the middle of this surface. Its long axis runs forward, downward, and out- 

 ward. It is convex in this direction. The upper inner end is the broader, and 

 near it the facet is \^ery often concave at right angles to the long axis, but in the 

 main it is about plane in that direction and may be even slightly convex. The anterior 

 facet, long and narrow, concave from before backward, runs forward and outward, 

 nearly parallel to the long axis of the former. It begins internally on the top of the 

 sustentaculum and ends at the most anterior point of the bone. In about half the 

 cases this surface is subdivided into two, and, as a rule, when it is not there is a 



* Calcaneus. 



