([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.

[Fig. 57].—Tibia and Fibula of Left Leg, Dorsal View.

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.