Part 9

_Calcaneus_ (Fig. 58, _a_, and Fig. 59).--The calcaneus (os calcis) is the largest bone of the foot and forms the heel. It is two or three times as long as broad and has six surfaces: dorsal, ventral, medial, lateral, proximal, and distal. The proximal one-half of the dorsal surface (Fig. 59) is smooth, while the distal half is broadened and bears two facets which are separated by a groove. These articulate with the corresponding facets on the astragalus. The medial facet is borne on a projection of the bone, the sustentaculum tali (_c_). Distad of the facets the surface is rough. The ventral surface is smooth. The proximal end (_b_) is grooved for the tendon of Achilles. The lateral surface is smooth and marked by a grooved tubercle, the =peroneal tubercle= (_d_), near the distal end. The medial surface is marked by part of the articular facet for the astragalus, and also by the grooved sustentaculum tali. The distal end (_a_) articulates with the cuboid.

[Illustration: FIG. 58.--TARSUS, METATARSUS, AND PHALANGES OF LEFT FOOT, VENTRAL VIEW.

_a_, calcaneus; _b_, astragalus; _c_, cuboid; _d_, scaphoid; _e_, lateral cuneiform; _g_, medial cuneiform; _h_, peroneal groove, for the tendon of the peroneus longus muscle; _i_, proximal phalanges; _j_, second row of phalanges; _k_, distal phalanges; _l_, sesamoid bones. 1, rudimentary first (medial) metatarsal; 2, 3, 4, 5, the other metatarsals.]

[Illustration: FIG. 59.--CALCANEUS OF RIGHT FOOT, DORSAL VIEW.

_a_, distal facet for cuboid; _b_, proximal end with groove for tendon of Achilles; _c_, sustentaculum tali; _d_, peroneal tubercle.]

_Cuboid._ _Os cuboideum_ (Fig. 58, _c_).--The cuboid has somewhat the form of a cube and articulates by its proximal end with the calcaneus (_a_), and by its distal end with the fourth and fifth metatarsals. Its medial surface articulates with the scaphoid (_d_) and lateral cuneiform (_e_). The ventral surface is marked near its distal end by an oblique ridge, distad of which is a deep groove, the peroneal groove (_h_), for the tendon of the peroneus longus muscle.

_Scaphoid._ (_Os naviculare pedis BNA_) (Fig. 58, _d_).--The scaphoid is a boat-shaped bone. Its proximal surface is marked by a concave facet for the head of the astragalus (_b_), and its distal surface has three facets for the lateral (_e_), intermediate and medial (_g_) cuneiform bones. At the junction of the ventral with the medial surface is a prominent tubercle. The lateral surface bears two linear facets for articulation with the calcaneus (_a_) and cuboid (_c_).

_Lateral Cuneiform._ _Ectocuneiform._ _Os cuneiforme tertium BNA_ (Fig. 58, _e_).--The lateral cuneiform is a wedge-shaped bone with a hooked process extending from the ventral sharp angle of the bone. It articulates by its proximal end with the scaphoid (_d_), and by its distal end with the third metatarsal. The medial surface bears near its distal end two facets for the second metatarsal, and on its proximal end a facet for the intermediate cuneiform. The caudal surface has a facet on its proximal end for the cuboid (_c_).

_Intermediate Cuneiform._ _Mesocuneiform._ _Os cuneiforme secundum BNA._--The intermediate cuneiform is small and wedge-shaped, with the base of the wedge dorsad. It lies between the lateral cuneiform and the medial cuneiform, articulates by its proximal end with the middle facet of the scaphoid, and bears on its distal end the second metatarsal. It is not visible in ventral view.

_Medial Cuneiform._ _Entocuneiform._ _Os cuneiforme primum BNA_ (Fig. 58, _g_).--The medial cuneiform lies on the medial side of the foot. It is a flat triangular bone about twice as long as broad, and broader at its proximal end than at the distal end. It bears on its distal end the rudimentary first metatarsal. The proximal end is oblique and bears a concave facet for the lateral distal facet of the scaphoid (_d_). The lateral surface has a concave facet at its proximal end for the intermediate cuneiform, while the distal portion is applied against the medial surface of the second metatarsal.

=Bones of the Foot or Pes= (Fig. 58).--_Metatarsals._ _Metatarsus_ (Fig. 58, 1-5).--The metatarsals are five in number. They bear a close resemblance to the metacarpals, but they may be distinguished by their bases.

The _first_ metacarpal (1) is rudimentary and conical. Its base has a facet for the distal end of the medial cuneiform (_g_), while the outer surface fits into a depression on the inner surface of the base of the second metatarsal.

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.

[Illustration: FIG. 60.--KNEE-JOINT, FROM THE DORSAL OR PATELLAR SIDE.

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.

The ligaments of the metatarsus and phalanges are of the same general character as in the forelimb. Of these Strauss-Durckheim enumerates thirty-six; they will not be described here.

THE MUSCLES.

=I. THE MUSCLES OF THE SKIN.= (Fig. 62.)

=M. cutaneus maximus= (Fig. 62, _b_).--This is a very large, thin muscle which covers almost the whole side of the body. It arises from the outer surface of the latissimus dorsi (Fig. 68, _m_) near its ventral end and from the bicipital arch (Fig. 65, _t′_) in the axilla; from the linea alba for a considerable distance (two or three inches) caudad of the base of the xiphoid process, and from the thorax over a line joining the axilla and the base of the xiphoid. Sometimes a few fibres take origin from the fascia which covers the pectoantibrachialis on the ventral side of the arm.

From their origin the fibres diverge. The cranial ones curve about the base of the forelimb and are inserted into the skin at or near the middle line caudad of the first thoracic vertebra. The most cranial fibres of all are inserted about one to one and a half centimeters from the middorsal line; thence the line of insertion approaches the middorsal line to reach it at about the eighth or ninth thoracic vertebra. The middle fibres run parallel to the middorsal line in the lumbar and sacral regions as far as the root of the tail, a small bundle passing onto the dorsal side of the tail, another onto the ventral side. The fibres of the caudal portion pass onto the thigh, the ventral ones running in the fold of skin which stretches from thigh to abdomen, and are finally lost in the fascia along a line connecting the knee and the root of the tail. A strong fascia connects the adjacent borders of the cutaneus and platysma and lies over the scapular region.

[Illustration: FIG. 62.--MUSCLES OF THE SKIN.

_a_, _a_′, _a_″, M. platysma; _b_, M. cutaneus maximus; _c_, M. orbicularis oris. Between the platysma and the cutaneus maximus are seen the following deeper muscles: _d_, M. acromio-trapezius; _e_, M. levator scapulæ ventralis; _f_, M. spino-deltoideus; _g_, M. acromio-deltoideus; _h_, M. clavobrachialis; _i_, caput laterale of M. triceps brachii; _j_, caput longum of M. triceps brachii; _k_, M. xiphi-humeralis; _l_, M. pectoralis minor. 1, external jugular vein.]

This muscle lies immediately beneath the integument. It covers the first layer of body muscles.

_Action._--Moves the skin.

=M. platysma= (Figs. 62 and 64, _a_, _a′_, _a″_).--This muscle forms a thin layer of fibres covering the sides of the neck and face, in close relation with the integument. Several more or less distinct portions may be distinguished.

(1) Most of the fibres (_a_) arise from the middorsal line, from the occiput to the first thoracic vertebra, in a narrow fascia common to the muscles of the two sides. The most cranial fibres of this region arise as a small bundle from the external occipital crest, beneath the levator auris longus (Fig. 63, _g_, _g′_).

From this origin in the middle line the fibres pass craniolaterad. The most cranial fibres curve about the ventral side of the ear and pass toward the caudal angle of the eye, where they unite with fibres of the zygomaticus (Fig. 64, _d_) or corrugator supercilii lateralis (Fig. 64, _k_), or pass to the lower eyelid. Caudad of these the fibres cover the side of the face and become lost among the facial muscles, some passing to the lower eyelid, some to the fibrous pad which supports the vibrissæ, some to the angle of the mouth, some to the lower lip. The most ventral fibres meet the fibres of the opposite muscle just ventrad of the symphysis of the mandible.

The ventral free border of the platysma is separated on the ventral side of the neck from the border of the opposite muscle by a wedge-shaped area having its point at the symphysis menti.

The fibres of this portion of the muscle are interrupted by an attachment to the skin, along a line passing from the base of the ear to about the middle of the coracoid border of the scapula, The dorsal (_a_) and ventral (_a′_) portions of the muscle, separated by this line of attachment, are sometimes described as separate muscles (the =supercervicocutaneus= and =cervicofacial=, respectively, of Strauss-Durckheim).