The ligamentum teres, or round ligament, is a very strong, short ligament which passes from the depression in the head of the femur to the bottom of the acetabulum.

The Knee-joint ([Figs. 60] and [61]).—The joint between the femur and the tibia is very complex. The surfaces of the condyles of the femur do not correspond to those of the condyles of the tibia. Between the ends of the two bones are placed two disks of cartilage, the menisci, or semilunar cartilages ([Fig. 60], c and d; [Fig. 61], a and b), of such a form that the congruity of articular surfaces is restored. Each meniscus has a proximal surface corresponding to the form of one of the condyles of the femur, and a distal surface corresponding to a condyle of the tibia. The menisci are held in position by ligaments. The knee-joint permits not only backward and forward movement, but also a small amount of rotary motion.

The joint has two capsules, one on the dorsal (convex) side, the other on the ventral side. The two communicate only by a small passageway lying within the joint between the ends of the bones. The dorsal one is attached to the femur several millimeters proximad of the patellar surface and some distance on each side of the latter. The patella is imbedded in its outer wall, and it is attached to the tibia on the edges of the articular surface of the latter, from the crest to the tuberosities. The capsule is also attached laterally and medially to the sides of the menisci, and is closely united to the patellar ligaments. Its cavity contains a mass of yellow fat.

The ventral capsule is attached to the borders of the articular surfaces of the femur and tibia on their ventral sides, to the menisci, and to the epicondyles of the femur and the tuberosities of the tibia. Its walls are stronger and its cavity smaller than those of the dorsal capsule.

The ligaments of the knee-joint ([Figs. 60] and [61]), aside from the capsules, may be classified into: (1) those which are connected with the patella; (2) collateral ligaments ([Fig. 60], i and j), which pass from the epicondyles directly distad along the sides of the joint to the tibia or fibula; (3) crucial ligaments ([Fig. 60], g and h; [Fig. 61], c and d), which cross within the joint from one side of the femur to the opposite side of the tibia; (4) ligaments which hold the menisci in place ([Fig. 60], e and f; [Fig. 61], e and f).

(1) Ligaments of the Patella.—The patella is imbedded in the dorsal wall of the dorsal capsule of the joint. From its distal end a strong tendon or ligament passes distad to the crest of the tibia. This is known as the ligamentum patellæ: it may be considered a part of the tendon of M. quadriceps femoris. On the lateral side the capsule of the joint is strengthened by the transverse fibres of the tendon of M. plantaris, which aid in holding the patella in place.

(2) Collateral Ligaments.—Of these there are two. The ligamentum collaterale fibulare ([Fig. 60], j) is attached to the lateral epicondyle of the femur and passes distad across the tendon of the plantaris muscle to the head of the fibula. Dorsad of the fibular ligament and parallel with it passes the tendon of origin of the extensor longus digitorum. The ligamentum collaterale tibiale ([Fig. 60], i; [Fig. 61], g) begins on the medial epicondyle of the femur and passes distad to the lateral tuberosity of the tibia; part of it passes one to one and a half centimeters distad of the tuberosity to be attached to a rough ridge on the side of the tibia.

[Fig. 60].—Knee-joint, from the Dorsal or Patellar Side.