[Fig. 61].—Knee-joint, from the Ventral or Flexor Side.

Fig. 60.—The patella has been removed. 1, femur; 2, tibia; 3, fibula. a, patellar surface of femur; b, tubercle for attachment of ligamentum patellæ; c, medial meniscus; d, lateral meniscus; e, f, ligaments of the menisci; g, ligamentum cruciatum anterius; h, ligamentum cruciatum posterius; i, ligamentum collaterale tibiale; j, ligamentum collaterale fibulare.

Fig. 61.—The capsule of the joint has been opened. 1, femur; 2, tibia (fibula not shown); 3, sesamoid bone in lateral head of M. gastrocnemius; 4, sesamoid in medial head of M. gastrocnemius; 5, tendon of M. popliteus, with sesamoid bone; 6, 7, lateral and medial condyles of the femur, with the intercondyloid notch between them; 8, 9, lateral and medial condyles of the tibia, with the popliteal notch between them; a, b, medial and lateral menisci; c, ligamentum cruciatum anterius; d, ligamentum cruciatum posterius; e, f, ligaments of the lateral meniscus; g, ligamentum collaterale tibiale.

(3) Crucial Ligaments.—There are two of these also. The ligamentum cruciatum anterius, or anterior crucial ligament ([Fig. 60], g; [Fig. 61], c), is a thick, strong ligament which begins on the dorsal part of the proximal end of the tibia nearer the medial side ([Fig. 60], g), and passes ventrad and proximad, between the ends of the two bones forming the joint, into the intercondyloid fossa of the femur, and becomes attached to the medial surface of the lateral condyle of the femur ([Fig. 61], c). It is composed of two partially separated bands, forming a slight angle with one another. It is crossed near its dorsal and ventral ends by two of the ligaments of the menisci. The ligamentum cruciatum posterius, or posterior crucial ligament ([Fig. 60], h; [Fig. 61], d), begins on the tibia at the edge of the popliteal notch ([Fig. 61], d), nearer the medial side, and passes dorsad and proximad to be attached to the ventral edge of the patellar surface of the femur, in the intercondyloid fossa ([Fig. 60], h).

(4) Ligaments of the Menisci.—There are five of these, connecting the menisci with the femur or tibia. One ([Fig. 60], e) passes from the dorsal edge of the medial meniscus (c) transversely across the anterior crucial ligament (g) to the proximal end of the tibia nearer the lateral side. A second ([Fig. 60], f) passes from the dorsal margin of the lateral meniscus (d) transversely beneath the anterior crucial ligament (g) to the proximal end of the tibia nearer the ventral side and medial border. A third ([Fig. 61], f) passes from the ventral margin of the lateral meniscus obliquely across the anterior crucial ligament (c) to the lateral side of the medial condyle of the femur. The fourth ([Fig. 61], e) is small, passing from the medial angle of the ventral border of the lateral meniscus distad to the popliteal notch. The fifth passes from the ventral border of the medial meniscus laterad beneath the posterior crucial ligament to the proximal end of the tibia, nearer the ventral and lateral sides.

Articulations between the Tibia and Fibula.—At the proximal end the fibula is as it were suspended from the distal side of the overhanging lateral tuberosity of the tibia by strong ligamentous tissue. The capsule of the joint is formed by an extension of the capsule of the knee-joint which passes between the tibia and fibula on the ventral side. Forming the dorsolateral wall of this extension is a strong, thick ligament which passes directly from the head of the fibula to the lateral surface of the lateral tuberosity of the tibia. A second more delicate ligament passes from the head of the fibula dorsoproximad to the tubercle laterad of the crest of the tibia, bridging a groove through which passes the tendon of M. extensor longus digitorum.

The tibia and fibula are connected throughout their length by an interosseus membrane. This is broad and very thin in its proximal part, narrower and thicker distad.

Distad the two malleoli forming the ends of the fibula and tibia are closely and immovably united. The capsule of the joint is here an extension proximad of the capsule of the articulation with the astragalus. On the dorsal side a short broad band of strong fibres passes from the surface of the tibia obliquely laterodistad to the border of the fibula; this forms the anterior ligament of the lateral malleolus. On the ventral side a very much weaker set of fibres forms the ventral wall of the articular capsule; it is called the posterior ligament of the lateral malleolus. Tibia and fibula are also connected on the dorsal side by the ligamentum transversum cruris, or transverse ligament of the lower leg ([Fig. 91], 5), which spans the tendons of Mm. extensor longus digitorum and tibialis anterior. From the middle of the distal margin of this a slender supporting ligament passes distad and is inserted on the dorsal surface of the tarsus. The grooves in the two malleoli for the passage of the tendons are spanned by ligamentous fibres (retinacula) for holding the tendons in place.

Articulation between the Leg and the Foot.—At the distal end there is formed between the two malleoli a deep irregular fossa, into which is received the trochlea of the astragalus. The joint is covered by a large articular capsule, which passes also, as above noted, between the tibia and fibula. In addition to the capsule the following ligaments may be distinguished: (a) On the lateral side, (1) a short ligament from the fibula to the astragalus, directed toward the proximal end of the foot; (2) a ligament from the fibula to the calcaneus, attached to the latter proximad of the peroneal tubercle; (3) a stronger ligament from the fibula to the calcaneus, lying beneath the last-mentioned and directed toward the proximal end of the bone. (b) On the medial side may be distinguished (1) a strong ligament from the tibia (medial malleolus) to the sustentaculum tali, and passing thence onto the scaphoid; (2) a short ligament from the medial malleolus to the astragalus.

The Tarsus.—The articulations between the separate bones of the tarsus and between the tarsus and metatarsus have a considerable number of variously communicating articular capsules. The separate bones are connected by many ligaments. The ligaments of the ventral surface (ligamenta plantaria) are especially well developed. Here may be noticed particularly a very large calcaneocuboid ligament, and a large calcaneocuneiform ligament which passes from the sustentaculum tali to the medial cuneiform. Those on the dorsal surface (ligamenta dorsalia) are less strong and numerous. Many ligaments, longitudinal, transverse, and oblique, pass also between the separate bones (ligamenta interossea). Ligamenta lateralia, on the lateral and medial borders of the foot, are also distinguishable. Strauss-Durckheim enumerates ninety-four ligaments of the tarsus; an account of each of these does not form part of the plan of the present work.