Part 19

The second (2). The proximal surface of the base is triangular, corresponding to the distal end of the intermediate cuneiform. The medial surface is marked by two concavities, one along the proximal border for the distal end of the medial cuneiform, and one distad of this for the first metatarsal. The lateral surface bears on the proximal margin an oblique triangular facet dorsad and a similar facet ventrad, both for the lateral cuneiform (e). Distad of these facets is a rough ridge.

The third (3). The proximal end of its base is a triangular facet with the apex directed ventrad and the sides excavated. It is for the distal end of the lateral cuneiform (e). Its medial surface presents a depression which receives the ridge of the second metatarsal. On the lateral surface a short distance distad of the proximal border is a triangular concave facet, and near the proximal border ventrad a second concave facet. Both are for the fourth metatarsal.

The fourth (4). The proximal end is convex, notched medially and facetted for the cuboid (c). Its medial surface bears dorsad, a short distance from its proximal end, a smooth tubercle, and ventrad a small convex facet. Both articulate with facets on the lateral surface of the third metatarsal. The lateral surface has a sinuous facet along its dorsal border, and ventrad of this a depression. There is a second facet along the ventral border. Both facets are for the fifth metatarsal, and the depression is for ligaments.

The fifth (5) has its base flattened and expanded so as to be wedge-shaped, with the apex of the wedge directed proximad. Its dorsal end extends into a tubercle. It thus presents only lateral and medial surfaces. The medial surface shows two tubercles, one distad of the other. The distal tubercle and the distal half of the proximal tubercle are facetted and fit into the sinuous facet on the fourth metatarsal. A narrow facet on the ventral border of the surface articulates with the facet on the ventral border of the lateral surface of the fourth metatarsal. The proximal half of the distal tubercle is facetted for the cuboid (c). The lateral surface is smooth, non-articular, and obliquely grooved.

Phalanges (Fig. 58, i, j, k).--There are three phalanges in each of the four digits, and these are almost identical with those described for the manus.

Sesamoid Bones. Ossa sesamoidea (Fig. 58, l).--The sesamoid bones are found at the joints between the metatarsals and phalanges, and are in all respects like those of the manus.

JOINTS AND LIGAMENTS OF THE PELVIC LIMBS.

Ligaments of the Pelvis.--The ilium and sacrum are articulated at the auricular facet of the ilium and the corresponding rough surface of the sacrum. The joint is an amphiarthrosis, permitting very little movement. A =capsular ligament= surrounds the articular surface, being attached to the bones about its circumference; it is short and strong. Craniad of the capsule is a thick very short ligament, composed of very strong transverse fibres passing from the rough surface of the sacrum to the corresponding rough surface of the ilium. This forms the =lateral iliosacral ligament=, which is united at its caudal border to the capsule.

A strong, wide ligamentous band passes from the dorsal border of the ilium to the sides of the sacrum. This is indistinctly subdivided into several bands, which together represent the =long= and =short posterior iliosacral ligaments= of man.

Symphysis pelvis.--The medial borders of the pubis and ilium meet in the middle line ventrad of the pelvis and are here united by cartilage. The joint is strengthened by numerous small bands which pass across the line of junction from one side to the other; these occur on both surfaces.

The Hip-joint.--The hip-joint is an =enarthrosis=, or ball-and-socket joint in which more than half the spherical head of the femur is received into the acetabulum. The depth of the acetabulum is increased by a rim of fibrocartilage about its margin, forming the =labrum glenoidale=. This passes across the acetabular notch, forming the =transverse ligament= of the acetabulum; beneath it blood-vessels and nerves pass into the acetabular cavity.

The =capsule of the joint= is large and loose. It is attached about the margin of the acetabulum, and passes over the head of the femur, to be attached to the bone several millimeters distad of the head. It thus encloses both the head and the neck of the femur.

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. 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.