342 



BONES OF THE FOOT. 



extremity has on its plantar portion two con- 

 cavities separated by a ridge, with which the 

 sesamoid bones articulate. The second cha- 

 racteristic is one which peculiarly distinguishes 

 this bone. 



The second is the longest ; it extends farther 

 backwards than any of the others, and is 

 lodged in a mortise-shaped cavity formed by 

 the three cuneiform bones. 



The fifth has the following characters : 1. 

 it is shorter than the second, third, and fourth ; 

 2. it has no lateral articular facet on the outer 

 side of its tarsal extremity ; 3. on this same side 

 it is prolonged backwards and outwards into 

 a long pyramidal process, which gives insertion 

 to the tendon of the peroneus brevis. This 

 process being quite subcutaneous, it is a useful 

 guide to surgeons in the partial amputation 

 of the foot at the tarso-metatarsal articulation. 



The third and fourth resemble each other 

 very closely; the thud, however, is a little 

 longer than the fourth, and the posterior ar- 

 ticular facet on the fourth is more quadrangular 

 than triangular. 



The structure of the metatarsal bones is that 

 of the long bones in general. 



Developement Each metatarsal bone has 

 two points of ossification ; one for the body, 

 the other for the anterior extremity, except 

 in the case of the first, in which the second 

 ossific point is for the tarsal extremity. Be- 

 tween the third and fourth months the osseous 

 point of the body commences, and in the 

 full-developed fcetus the body is completely 

 ossified. In the course of the second year 

 the point for the extremity appears ; the epi- 

 physis of the first metatarsal bone is united 

 first, about the eighteenth year, and this union 

 precedes that of the others by about twelve 

 months. 



Toes(Digiti pedis; Fr. les orteils ; Germ. 

 die Zehen). The toes are numbered from the 

 inner or great toe; they gradually diminish in 

 length from the first to the fifth : the four 

 outer ones consist each of three portions or 

 phalanges; the great toe has only two. The 

 phalanges are best named from their relations, 

 viz. metatarsal, middle, and ungual. 



The metatarsal phalanges are considerably 

 the longest. 1'he shaft in each is prismatic, like 

 that of the metatarsal bones, convex on the dor- 

 sal, concave on the plantar surface. On the pos- 

 terior extremity is a concave facet, articulated 

 with the anterior head or condyle of the cor- 

 responding metatarsal bone. The anterior ex- 

 tremity is less swollen than the posterior: it 

 is marked by an articular surface, which ex- 

 tends much more on the inferior surface than 

 the superior; this is concave transversely, but 

 convex from above downwards, and is arti- 

 culated with the posterior extremity of the 

 middle phalanx. All the metatarsal phalanges 

 possess these general characters: that of the 

 great toe is very considerably thicker than the 

 others, and is slightly longer; the remaining 

 ones differ but little in size : they progressively 

 diminish towards the fifth. 



The middle phalanges are very short, but 

 possess pretty nearly the same general characters 



as the metatarsal. The posterior extremities 

 are articulated with the last-named phalanges 

 by means of an articular surface, concave 

 from before backwards and convex transversely. 

 The articular surface on the anterior extremity 

 is convex. The great toe is deficient in the 

 middle phalanx; they diminish in size from 

 within and outwards. They have been com- 

 pared to the pieces of the coccyx, but may 

 be easily distinguished by the articular surfaces. 



The ungual phalanges (so called from being 

 next the nail, unguis) are five in number, 

 and decrease in size from the first to the fifth ; 

 that belonging to the first very much exceeding 

 the rest in size. The posterior extremity of 

 each is expanded, and has an articular facet 

 for articulation with the middle phalanx. The 

 central part or shaft is flattened, slightly 

 convex on its dorsal surface : its anterior ex- 

 tremity is still more flattened and slightly 

 expanded, presenting a thin convex margin. 

 It is rough on its inferior surface where the 

 dense and adipose cellular tissue constituting 

 the pulp of the toe is connected with it, and 

 on its superior surface it is smooth, where 

 the nail is applied upon it. 



The structure and mode of developement 

 of the phalanges are pretty much the same 

 as those of the metatarsal bones : their complete 

 ossification, however, takes place at a much 

 later period. 



For the modifications in the number, forms, 

 and arrangement of the bones cf the foot in 

 the animal series, see OSSEOUS SYSTEM (Comp. 

 Anat.) and the articles on the various classes. 



JOINTS OF THE FOOT. These may be classed 

 as the joints of the tarsus, metatarsus, and 

 toes. 



Joints of the tarsus. The bones constituting 

 the first row of the tarsus are connected to- 

 gether by means of two articulations, one 

 posterior, the other anterior. The first (pos- 

 terior astragalo - calcanien articulation) is 

 formed by a convex oval surface on the os 

 calcis, which is received into a deep concavity 

 on the astragalus. A synovial sac lines these 

 surfaces; the posterior part of this sac is 

 covered by the fatty substance which is placed 

 between the back of the ankle-joint and the 

 tendo Achillis, and on the removal of the fat 

 the sac is observed to be strengthened, especially 

 in its centre, by a few ligamentous fibres. 

 On the inner side this sac is strengthened by 

 the tendon of the flexor pollicis proprius and 

 its sheath behind, and by the internal lateral 

 ligament of the ankle-joint in front ; both of 

 which very much protect the articulation and 

 strengthen the union of the bones. Anteriorly 

 there are no proper fibres applied upon the 

 synovial membrane; but the interosseous liga- 

 ment to be described presently, amply supplies 

 the want of them. On the outside a few 

 ligamentous fibres are applied to the synovial 

 membrane. 



The anterior astragalo-calcanien articulation 

 is formed by a slightly convex surface on the 

 astragalus, which is received by a concavity 

 on the upper surface of the sustentaculum of 

 the os calcis. This articulation is furnished 



