Part 18

a, head; b, neck; c, depression for round ligament; d, great trochanter; e, trochanteric fossa; f, intertrochanteric line; g, lesser trochanter; h, linea aspera; i, medial condyle; j, lateral condyle; k, intercondyloid fossa; l, lateral epicondyle.]

=Femur= (Fig. 56).--The femur is the proximal bone of the posterior extremity. It consists of enlarged proximal and distal ends connected by a nearly cylindrical shaft. The proximal end presents on its medial side a hemispherical =head= (a) which fits into the acetabulum. It is supported by a =neck= (b) which is contracted near the head and expanded dorsoventrally where it joins the remainder of the bone. The medial surface of the head presents near its ventral border a depression (c) for the insertion of the round ligament of the femur. Ventrad the articular surface of the head extends as an acute projection onto the shaft, so that the whole articular surface appears somewhat pear-shaped. On the lateral side of the proximal end opposite the head is a projecting mass, the =great trochanter= (d), forming the end of the shaft. On the medial side of the great trochanter at its junction with the neck is a deep fossa, the =trochanteric= fossa or =digital= fossa (e) for the insertion of muscles. From the ventral surface of the great trochanter a ridge, the =intertrochanteric= line (f), is continued distad, ending in a pyramidal projection, the =lesser trochanter= (g), which serves for the insertion of muscles. A second ridge is continued to the lesser trochanter from the neck. A slight but well-marked ridge, the =spiral= ridge or line, runs round two sides of the neck parallel to the second ridge.

The shaft is nearly straight and cylindrical. A rough line is continued along its ventral surface from the lesser trochanter, and a similar line along its lateral surface from the greater trochanter; these unite ventrad to form the =linea aspera= (h). On its ventral surface is a nutrient foramen, directed proximad.

The shaft gradually widens distad and ends in two =condyles= (i and j) which are continuous dorsad but separated ventrad by a deep notch, the =intercondyloid fossa= (k). The distal surface of the shaft and condyles is articular. This articular surface is larger on the lateral condyle (j). The part of the articular surface on the end of the shaft (=patellar surface=) is for the patella; that part of it on the condyles and separated by the notch is for the tibia.

On the lateral surface of the lateral condyle is a slight prominence, the lateral epicondyle (l), and on the medial surface of the medial condyle is another prominence, the medial epicondyle; both are for the attachment of ligaments.

=Patella= (Fig. 1, r).--The patella is a small flat bone with a pear-shaped outline, having its apex distad. It lies against the articular surface at the lower end of the shaft of the femur. It thus covers the knee-joint. The inner surface is smooth and convex from side to side, but concave in a proximodistal line. It fits against the lower end of the femur. Its outer surface is rough and concave. It is a sesamoid bone inserted in the tendon of the quadriceps femoris muscle.

Three other sesamoid bones are found in the region of the knee (see Fig. 61, p. 89). Two are in the tendons of the gastrocnemius muscle, proximad of the two condyles of the femur. The third is in the tendon of the popliteus muscle, just laterad of the lateral condyle of the femur.

I, tibia; II, fibula. a, medial condyle of the tibia; b, lateral condyle; c, spine of the tibia; d, crest of the tibia; e, tubercle for attachment of the patellar ligament; f, medial malleolus; g, projection of dorsal surface of the tibia; h, head of fibula; i, lateral malleolus.]

=Tibia= (I, Fig. 57).--The tibia is the longer of the two bones of the leg between the knee and the ankle, and is the longest bone of the body. It has a triangular shaft and enlarged proximal and distal ends.

The proximal end is curved ventrad and projects into two prominences, the =tuberosities=, on either side. Each tuberosity bears on its proximal end an articular facet for the condyles of the femur; these are known respectively as the =lateral= and =medial condyles= (a and b) of the tibia. The condyles are oval, convex dorsoventrad, and concave from side to side. The two condyles are separated at the middle of their contiguous margins by a bicuspid projection, the =spine= of the tibia (c). They are continuous dorsad, but separated ventrad by a deep notch between the tuberosities, the =popliteal= notch. On the distal side of the lateral condyle is an elongated facet for the proximal end of the fibula.

The shaft is triangular, smallest at about its middle and enlarged at both ends. It presents dorsal, medial, and lateral borders, and medial, lateral, and ventral surfaces. The lateral surface is concave proximad. The medial surface is convex. The two are continuous at the distal end. At their proximal ends the border separating them is raised into a prominent ridge, the =crest= (d) of the tibia, the proximal end of which contributes to increase the proximal surface of the bone, and presents an oblong tubercle (e) for the insertion of the =ligamentum patellæ= (ligament of the quadriceps femoris muscle). The ventral surface is concave proximad where it abuts upon the tuberosities. Its proximal half is crossed by two rough parallel lines, the distal one of which crosses in a spiral course from the lateral to the medial border; near its beginning is a nutrient foramen.

The distal end extends farther distad on its medial side. The extension is the =medial malleolus= (f). The malleolus presents two grooves on its medial surface for the tendons of muscles. On the lateral side of the distal end is an oblique triangular facet for the distal end of the fibula. The ventral surface of the distal end presents an oblique border which passes from the apex of the malleolus proximolaterad. The dorsal surface extends into a V-shaped projection (g) between the malleolus and the fibular facet. The distal end presents an oblique ridge running from the apex of the V-shaped extension of the dorsal surface to near the base of the medial malleolus. The ridge and the concavities on either side of it, the medial one of which is deeper, fit against the proximal trochlear surface of the astragalus.

=Fibula= (II, Fig. 57).--The fibula lies at the lateral side of the tibia in the shank. It is a slender triangular bone with enlarged proximal and distal ends.

The proximal end or head (h) is flattened. It bears a facet on its proximomedial surface for articulation with the tibia, and is longitudinally grooved on the outer surface.

The shaft has a very sharp medial border. This border is turned toward the tibia and gives attachment to the interosseous membrane, which runs between the tibia and fibula.

The distal end is expanded to form the =lateral malleolus= (i). This bears a facet on the proximal portion of its medial surface near its dorsal margin, for the tibia, and distad of this is a second facet for the astragalus. The ventral and lateral surfaces are grooved for tendons.

=Tarsus= (Fig. 58).--The tarsus consists of seven bones. The longest of these, lying on the lateral side of the foot and forming the support of the heel, is the =calcaneus= or =os calcis= (a). It articulates distad with a bone, the =cuboid= (c), which bears the fourth and fifth metatarsals. Lying between the calcaneus and the tibia is the =astragalus= or =talus= (b), the distal end of which articulates with the boat-shaped =navicular= or =scaphoid= (d). The scaphoid bears on its distal surface the three cuneiform bones, lateral (e), medial (g), and intermediate, bearing the rudiment of the first metatarsal and the second and third metatarsals.

Astragalus. (Talus BNA) (Fig. 58, b).--The astragalus may be divided into body, neck, and head. The body is marked on its proximal surface by a deep pulley-like groove for the articulation with the distal end of the tibia, and on its lateral and medial surfaces by curved facets for articulation with the malleoli of the tibia and fibula. This entire surface for articulation with the bones of the leg is known as the trochlea. The lower surface is marked by two facets separated by a groove; these are for articulation with corresponding facets on the calcaneus. Distally the bone contracts to form the =neck= and enlarges at the end, forming the =head=, which is smooth on its distal surface for articulation with the navicular or scaphoid.

Calcaneus (Fig. 58, a, and Fig. 59).--The calcaneus (os calcis) is the largest bone of the foot and forms the heel. It is two or three times as long as broad and has six surfaces: dorsal, ventral, medial, lateral, proximal, and distal. The proximal one-half of the dorsal surface (Fig. 59) is smooth, while the distal half is broadened and bears two facets which are separated by a groove. These articulate with the corresponding facets on the astragalus. The medial facet is borne on a projection of the bone, the sustentaculum tali (c). Distad of the facets the surface is rough. The ventral surface is smooth. The proximal end (b) is grooved for the tendon of Achilles. The lateral surface is smooth and marked by a grooved tubercle, the =peroneal tubercle= (d), near the distal end. The medial surface is marked by part of the articular facet for the astragalus, and also by the grooved sustentaculum tali. The distal end (a) articulates with the cuboid.

a, calcaneus; b, astragalus; c, cuboid; d, scaphoid; e, lateral cuneiform; g, medial cuneiform; h, peroneal groove, for the tendon of the peroneus longus muscle; i, proximal phalanges; j, second row of phalanges; k, distal phalanges; l, sesamoid bones. 1, rudimentary first (medial) metatarsal; 2, 3, 4, 5, the other metatarsals.]

a, distal facet for cuboid; b, proximal end with groove for tendon of Achilles; c, sustentaculum tali; d, peroneal tubercle.]

Cuboid. Os cuboideum (Fig. 58, c).--The cuboid has somewhat the form of a cube and articulates by its proximal end with the calcaneus (a), and by its distal end with the fourth and fifth metatarsals. Its medial surface articulates with the scaphoid (d) and lateral cuneiform (e). The ventral surface is marked near its distal end by an oblique ridge, distad of which is a deep groove, the peroneal groove (h), for the tendon of the peroneus longus muscle.

Scaphoid. (Os naviculare pedis BNA) (Fig. 58, d).--The scaphoid is a boat-shaped bone. Its proximal surface is marked by a concave facet for the head of the astragalus (b), and its distal surface has three facets for the lateral (e), intermediate and medial (g) cuneiform bones. At the junction of the ventral with the medial surface is a prominent tubercle. The lateral surface bears two linear facets for articulation with the calcaneus (a) and cuboid (c).

Lateral Cuneiform. Ectocuneiform. Os cuneiforme tertium BNA (Fig. 58, e).--The lateral cuneiform is a wedge-shaped bone with a hooked process extending from the ventral sharp angle of the bone. It articulates by its proximal end with the scaphoid (d), and by its distal end with the third metatarsal. The medial surface bears near its distal end two facets for the second metatarsal, and on its proximal end a facet for the intermediate cuneiform. The caudal surface has a facet on its proximal end for the cuboid (c).

Intermediate Cuneiform. Mesocuneiform. Os cuneiforme secundum BNA.--The intermediate cuneiform is small and wedge-shaped, with the base of the wedge dorsad. It lies between the lateral cuneiform and the medial cuneiform, articulates by its proximal end with the middle facet of the scaphoid, and bears on its distal end the second metatarsal. It is not visible in ventral view.

Medial Cuneiform. Entocuneiform. Os cuneiforme primum BNA (Fig. 58, g).--The medial cuneiform lies on the medial side of the foot. It is a flat triangular bone about twice as long as broad, and broader at its proximal end than at the distal end. It bears on its distal end the rudimentary first metatarsal. The proximal end is oblique and bears a concave facet for the lateral distal facet of the scaphoid (d). The lateral surface has a concave facet at its proximal end for the intermediate cuneiform, while the distal portion is applied against the medial surface of the second metatarsal.

=Bones of the Foot or Pes= (Fig. 58).--Metatarsals. Metatarsus (Fig. 58, 1-5).--The metatarsals are five in number. They bear a close resemblance to the metacarpals, but they may be distinguished by their bases.

The first metacarpal (1) is rudimentary and conical. Its base has a facet for the distal end of the medial cuneiform (g), while the outer surface fits into a depression on the inner surface of the base of the second metatarsal.