Femur.—The femur or thigh-bone (fig. 16) is the longest bone in the body, and consists of a shaft and two extremities. The upper extremity or head has a smooth hemispherical surface, in which an oval roughened fossa, for the attachment of the liga mentum teres of the hip, is found ; from the head a strong elon gated neck passes downward and outward to join the upper end of the shaft ; the place of junction is marked by two processes or trochanters ; to the external or great trochanter are attached many muscles; the internal or lesser trochanter gives attachment to the psoas and iliacus. A line drawn through the axis of the head and neck forms with a vertical line drawn through the shaft an angle of 3o° ; in a woman this angle is a little less obtuse, and the ob liquity of the shaft of the femur is slightly greater. The shaft is almost cylindrical about its centre, but expanded above and below; its front and sides give origin to the extensor muscles of the leg; behind there is a rough ridge, which gives attachment to several muscles. The lower end of the bone presents a large smooth artic ular surface for the knee-joint, the anterior portion of which forms a trochlea or pulley for the movements of the patella, whilst the lower and posterior part is subdivided into two convex condyles by a deep fossa which gives attachment to the crucial ligaments of the knee.
The femur constitutes usually about 0.275 of the individual stature ; but this proportion is not constant, as this bone forms a larger element in the stature of a tall than of a short man. The human femur presents also a concave popliteal surface, thus dif fering from that of Pithecanthropus, whose popliteal surface is convex. In the bones of some races the dorsal ridge of the thigh bone (lines aspera) projects as a prominent crest causing the bones to appear "pilastered." Pilastering, though characteristic of lower and primitive races of man, is never found in the an thropoids.
Patella.—The patella or knee-cap (fig. 16) is a triangular flat tened bone developed in the tendon of the great extensor muscles of the leg. Its anterior surface and sides are rough, for the attach ment of the fibres of that tendon ; its posterior surface is smooth, and enters into the formation of the knee-joint.
Between the two bones of the leg there are no movements of pronation and supination as between the two bones of the fore arm. The tibia and fibula are fixed in position ; the fibula is al ways external, the tibia internal.
Tibia.—The tibia or shin-bone (fig. i6) is the larger of the two bones of the leg; the femur moves and rests upon its upper end, and down it the weight of the body in the erect position is trans mitted to the foot. Except the femur, it is the longest bone of the skeleton, and consists of a shaft and two extremities. The upper
extremity is broad, and is expanded into two tuberosities, the ex ternal of which has a small articular facet inferiorly, for the head of th4 fibula ; superiorly, the tuberosities have two smooth sur faces, for articulation with the condyles of the femur; they are separated by an intermediate rough surface, from which a short spine (really a series of elevations) projects, which gives attachments to the interarticular crucial ligaments and semilunar cartilages of the knee, and lies opposite the intercondylar fossa of the femur. The shaft of the bone is three-sided ; its inner sur face is subcutaneous, and forms the shin; its outer and posterior surfaces are for the origin of muscles; the anterior border forms the sharp ridge of the shin, and terminates superiorly in a tubercle for the insertion of the extensor tendon of the leg; the outer bor der of the bone gives attachment to the interosseous membrane of the leg. The lower end of the bone, smaller than the upper, is prolonged into a broad process, internal malleolus, which forms the inner prominence of the ankle : its under surface is smooth for articulation with the astragalus; externally it articulates with the lower end of the fibula.
The tibia in most civilized races is triangular in the section of its shaft, but in many savage and prehistoric races it is two-edged. The foetal tibia has its head slightly bent backward with regard to the shaft, a condition which usually disappears in the adult, but is shown in the prehistoric tibiae found in the cave of Spy. In races that squat on their heels the front margin of the lower end of the tibia is marked by a small articular facet for the neck of the astragalus.
Fibula.—The fibula, or splint-bone of the leg (fig. i6), is a slender long bone with a shaft and two extremities. The upper end or head articulates with the outer tuberosity of the tibia. The shaft is four-sided and roughened for the origins of the muscles. Separating the anterior from the internal surface is a slender ridge for the attachment of the interosseous membrane. The lower end has a strong process (external malleolus) projecting downward to form the outer prominence of the ankle, and a smooth inner sur face for articulation with the astragalus, above which is a rough surface for the attachment of ligaments which bind together the tibia and fibula.