Chapter VI: Bones of the Pelvic Extremities (1)

=Innominate Bones. Ossa innominata.= (=Os coxæ BNA=) (Figs. 54 and 55).--The two innominate bones articulate with the sacrum and extend thence caudoventrad and finally turn mediad and unite in the middle line, forming the =symphysis pubis=. They thus form an arch, =the pelvic arch=, =pelvic girdle= or =pelvis=, which is closed dorsad by the sacrum.

In the middle of the lateral surface of each bone is a hemispherical depression, the =acetabulum= (Fig. 55, _d_), which receives the head of the femur.

_I_, ilium; _II_, ischium; _III_, pubis; _IV_, acetabular bone. _a_,
acetabulum; _b_, obturator foramen.]

In the kitten each innominate bone is composed of three principal parts united by sutures (Fig. 54). From the sacrum to the acetabulum is a single bar, the =ilium= (_I_). Caudad of the acetabulum are two bars. The dorsal one of these is the =ischium= (_II_), and the ventral one is the =pubis= (_III_). The ischium enters into the formation of the acetabulum (_a_), but the pubis does not. The two bones, however, are in contact at the ventral edge of the acetabulum. From this point they diverge, but unite with one another again near the middle line and thus enclose an oval foramen, the =obturator foramen= (_b_). Wedged between the ilium, ischium, and pubis at their point of junction and helping to form the acetabulum is a small irregular bone, the =acetabular bone= (_IV_). In the adult cat these four parts are united into a single bone which is nevertheless usually described, ignoring the acetabular piece, as made up of ilium (Fig. 55, _I_), ischium (_II_), and pubis (_III_).

_I_, ilium; _II_, ischium; _III_, pubis. _a_, crest of the ilium; _b_,
posterior inferior spine; _c_, great sciatic notch; _d_, acetabulum;
_d′_, incisura acetabuli; _e_, spine of the ischium; _f_, lesser
sciatic notch; _g_, tuberosity of the ischium; _h_, ramus of the
ischium; _i_, ramus of the pubis; _j_, obturator foramen; _k_, pubic
tubercle; _l_, iliopectineal line; _l′_, ilio-pectineal eminence; _m_,
anterior superior process.]

The =ilium= (_I_) is somewhat contracted at the middle and broader at its ends. One end enters into the acetabulum (Fig. 55, _d_) and forms about one-fifth the articular surface. This end is also the thickest part of the bone. The lateral surface of the ilium is concave for the attachment of muscles. The medial surface is smooth over its acetabular half and rough over its sacral half. The rough portion is marked at its junction with the smooth portion by the ear-shaped =auricular impression= by which the bone articulates directly with the sacrum. The caudal half of that part of the medial surface craniad of the auricular impression gives attachment to the ilio-sacral ligaments which bind the ilium to the sacrum. The dorsal border is straight at its cranial end and concave and rounded at its caudal end. Between the two portions and at the dorsal edge of the auricular surface is a protuberance corresponding to the =posterior inferior spine= (Fig. 55, _b_) of the human ilium. The concavity of the dorsal border (_c_) corresponds to the great sciatic notch of the human ilium. At its caudal end is the short =spine of the ischium= (_e_), which is not a part of the ilium. The ventral border of the ilium is broad caudad, becoming narrower craniad. The lateral margin of the ventral border is continued to a tuberosity at the edge of the acetabulum; its medial margin is called the =iliopectineal line= (_l_) and extends on the pubis to the symphysis. An eminence, the =iliopectineal eminence= (_l′_), on the iliopectineal line, lies opposite to the acetabulum at about the junction of the ilium and pubis. The cranial end of the bone is thickened, forming the =crest= (_a_) of the ilium. At the junction of the crest with the ventral border is a projection, the =anterior superior process= (_m_) of human anatomy.

The =pubis= (_III_) (including the acetabular bone) enters into the formation of the acetabulum (_d_) constituting about one-sixth the circumference, but less than one-sixth its area. It may be described as a flat, curved bone, contracted at the middle and expanded at the ends. The dorsal end enters into the acetabulum; the ventral end unites with the opposite bone at the symphysis pubis and sends caudad a projection, the =ramus= (_i_) of the pubis, which unites with the ramus of the opposite bone to form about two-thirds of the entire symphysis. At the sides of the symphysis a slightly marked angle projects craniad from each of the pubic bones; these two together constitute the =pubic tubercle= (_k_), for the origin of the rectus abdominis muscle. The surfaces of the ramus are smooth. One of its borders is concave and enters into the formation of the obturator foramen (_j_). Another of its borders is the iliopectineal line (_l_). Its third border is rough for the symphysis.

The =ischium= (_II_) has the form of a triangular prism contracted at the middle. Its cranial end forms nearly two-thirds of the acetabulum. Its caudal end bears dorsad a rough thickening, the =tuberosity= of the ischium (_g_). From the caudal half of the ventral border of the bone a sickle-shaped process, the =ramus= (_h_) of the ischium, curves medioventrad and then craniad and joins the ramus of the pubis. Its medial border is rough and enters into the symphysis, forming the caudal one-third. The lateral angle of the bone is rounded. Its dorsal angle is marked near the cranial end by the =spine= (_e_) of the ischium. The concavity between this spine and the tuberosity corresponds to the =lesser sciatic notch= (_f_) of human anatomy.

The acetabulum (_d_) is cup-shaped. The ventral one-sixth of its border is deficient and a broad groove extends from the deficiency to the bottom of the cup. The deficiency, =incisura acetabuli=, or =acetabular notch= (_d′_), is closed naturally by a ligament, and the groove gives origin to the ligament (ligamentum teres) which attaches the head of the femur.

_a_, head; _b_, neck; _c_, depression for round ligament; _d_, great
trochanter; _e_, trochanteric fossa; _f_, intertrochanteric line; _g_,
lesser trochanter; _h_, linea aspera; _i_, medial condyle; _j_,
lateral condyle; _k_, intercondyloid fossa; _l_, lateral epicondyle.]

=Femur= (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.

_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.]

=Tibia= (_I_, Fig. 57).--The tibia is the longer of the two bones of the leg between the knee and the ankle, and is the longest bone of the body. It has a triangular shaft and enlarged proximal and distal ends.

The proximal end is curved ventrad and projects into two prominences, the =tuberosities=, on either side. Each tuberosity bears on its proximal end an articular facet for the condyles of the femur; these are known respectively as the =lateral= and =medial condyles= (_a_ and _b_) of the tibia. The condyles are oval, convex dorsoventrad, and concave from side to side. The two condyles are separated at the middle of their contiguous margins by a bicuspid projection, the =spine= of the tibia (_c_). They are continuous dorsad, but separated ventrad by a deep notch between the tuberosities, the =popliteal= notch. On the distal side of the lateral condyle is an elongated facet for the proximal end of the fibula.

The shaft is triangular, smallest at about its middle and enlarged at both ends. It presents dorsal, medial, and lateral borders, and medial, lateral, and ventral surfaces. The lateral surface is concave proximad. The medial surface is convex. The two are continuous at the distal end. At their proximal ends the border separating them is raised into a prominent ridge, the =crest= (_d_) of the tibia, the proximal end of which contributes to increase the proximal surface of the bone, and presents an oblong tubercle (_e_) for the insertion of the =ligamentum patellæ= (ligament of the quadriceps femoris muscle). The ventral surface is concave proximad where it abuts upon the tuberosities. Its proximal half is crossed by two rough parallel lines, the distal one of which crosses in a spiral course from the lateral to the medial border; near its beginning is a nutrient foramen.

The distal end extends farther distad on its medial side. The extension is the =medial malleolus= (_f_). The malleolus presents two grooves on its medial surface for the tendons of muscles. On the lateral side of the distal end is an oblique triangular facet for the distal end of the fibula. The ventral surface of the distal end presents an oblique border which passes from the apex of the malleolus proximolaterad. The dorsal surface extends into a V-shaped projection (_g_) between the malleolus and the fibular facet. The distal end presents an oblique ridge running from the apex of the V-shaped extension of the dorsal surface to near the base of the medial malleolus. The ridge and the concavities on either side of it, the medial one of which is deeper, fit against the proximal trochlear surface of the astragalus.

=Fibula= (_II_, Fig. 57).--The fibula lies at the lateral side of the tibia in the shank. It is a slender triangular bone with enlarged proximal and distal ends.

The proximal end or head (_h_) is flattened. It bears a facet on its proximomedial surface for articulation with the tibia, and is longitudinally grooved on the outer surface.

The shaft has a very sharp medial border. This border is turned toward the tibia and gives attachment to the interosseous membrane, which runs between the tibia and fibula.

The distal end is expanded to form the =lateral malleolus= (_i_). This bears a facet on the proximal portion of its medial surface near its dorsal margin, for the tibia, and distad of this is a second facet for the astragalus. The ventral and lateral surfaces are grooved for tendons.

=Tarsus= (Fig. 58).--The tarsus consists of seven bones. The longest of these, lying on the lateral side of the foot and forming the support of the heel, is the =calcaneus= or =os calcis= (_a_). It articulates distad with a bone, the =cuboid= (_c_), which bears the fourth and fifth metatarsals. Lying between the calcaneus and the tibia is the =astragalus= or =talus= (_b_), the distal end of which articulates with the boat-shaped =navicular= or =scaphoid= (_d_). The scaphoid bears on its distal surface the three cuneiform bones, lateral (_e_), medial (_g_), and intermediate, bearing the rudiment of the first metatarsal and the second and third metatarsals.

_Astragalus._ (_Talus BNA_) (Fig. 58, _b_).--The astragalus may be divided into body, neck, and head. The body is marked on its proximal surface by a deep pulley-like groove for the articulation with the distal end of the tibia, and on its lateral and medial surfaces by curved facets for articulation with the malleoli of the tibia and fibula. This entire surface for articulation with the bones of the leg is known as the trochlea. The lower surface is marked by two facets separated by a groove; these are for articulation with corresponding facets on the calcaneus. Distally the bone contracts to form the =neck= and enlarges at the end, forming the =head=, which is smooth on its distal surface for articulation with the navicular or scaphoid.

_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.

_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.]

_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.

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.

_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).

(2) A band of fibres one or two centimeters across (_a″_) arises in the fascia of the side of the neck just craniad of the middle of the coracoid border of the scapula, and passes caudoventrad toward the manubrium, its fibres crossing the fibres of the first part of the platysma at right angles. These fibres become lost in the fascia ventrad of the manubrium, or pass across the middle line to intermingle with the corresponding fibres of the opposite side. This portion of the platysma is sometimes absent.

The platysma is everywhere subcutaneous, except at its dorsocranial angle, where a small bundle of fibres is covered by the levator longus auris. It covers the deeper muscles of the neck and head. Closely attached to its inner surface are the submentalis and depressor conchæ, whose fibres bridge over the ventral interval between the borders of the platysmas of opposite sides.

_Action._--Moves the skin of the face and neck.

=II. THE MUSCLES OF THE HEAD.=

A. SUPERFICIAL MUSCLES.--The most superficial layer of muscles on the face and head is formed by differentiation of the fibres of the platysma. The muscles thus formed are not clearly distinct from each other; in this region sets of fibres differing in direction and in origin or insertion receive separate names even though the different sets of fibres are closely interwoven.

In the quadrangle on the dorsal surface of the head enclosed between the two eyes and the two ears, a thin superficial sheet of fibres is found, in which a number of different sets may be distinguished (Fig. 63). These have received the following names.

=M. intermedius scutulorum= (Fig. 63, _a_).--This consists of a broad thin sheet of transverse fibres between the two external ears. The fibres are attached at either end to the scutiform cartilage (1) of the two ears, and pass without interruption across the middle line. At its cranial edge this muscle is continuous with the corrugator supercilii medialis (_b_); at its lateral edge with the frontoscutularis; at its caudal edge with the levator auris longus (_g_).

_Relations._--Outer surface with the integument. Inner surface with the galea aponeurotica (to which the muscle is closely united), the epicranius muscle (_h_) and the temporal muscle (_n_).

_Action._--Draws the two ears dorsad, toward the middle line.

On the right side are shown the superficial muscles; on the left side
the superficial muscles have mostly been removed, exposing the deeper
muscles and the bone. _a_, M. intermedius scutulorum; _b_, M.
corrugator supercilii medialis; _c_, M. orbicularis oculi; _d_, M.
corrugator supercilii lateralis; _e_, cranial end fibres of M.
platysma; _f_, M. adductor auris superior; _g_, _g′_, M. levator auris
longus (_g_, cranial portion; _g′_, caudal portion); _h_, _h′_, M.
epicranius (_h_, M. occipitalis; _h′_ M. frontalis); _i_, M.
transversus auriculæ; _k_, M. auricularis superior (cut on the left
side); _l_, M. abductor auris brevis; _m_, M. abductor auris longus;
_n_, M. temporalis; _o_, cut origin of M. frontoscutularis; _p_, _p′_,
M. levator labii superioris alæque nasi (_p′_, the origin from the
maxillary bone); _q_, angular head of M. quadratus labii superioris.
1, scutiform cartilage; 2, external ear; 3, bones of the skull.]

=M. corrugator supercilii medialis= (_b_).--This consists of a thin sheet of scattered fibres lying craniad of the last and intermingling with it. The fibres take origin near the middle line, pass laterad, then curve craniad, converging, to be inserted into the whole extent of the upper eyelid, especially near the caudal angle. Here the fibres unite with those of the orbicularis oculi (_c_).

This muscle is continuous caudad with the intermedius scutulorum (_a_), craniad with the orbicularis oculi (_c_); laterad with the corrugator supercilii lateralis (_d_). Toward the medial side the fibres lose themselves in a tendinous sheet that joins the galea aponeurotica.

_Relations._--Outer surface with the integument. Inner surface with the frontoscutularis and the skull.

_Action._--Raises the upper eyelid.

=M. orbicularis oculi= (Fig. 63, _c_; Fig. 64, _s_).--This consists of two thin bands of muscle-fibres which lie one in either eyelid parallel to its border and unite at the angle of the eye.

_Origin_ by short tendon-fibres from a tubercle on the surface of the frontal process of the maxillary bone just dorsad of the orbital end of the lachrymal canal and between the two parts of the quadratus labii superioris (Fig. 63, _p_ and _q_).

The muscle splits into two parts which pass into the two eyelids. At the outer angle of the eye the two bands unite by the intervention of tendon-fibres between the muscle-fibre bundles of the two.

_Relations._--Outer surface with the integument. Inner surface with the inner membrane of the eyelid.

_Action._--Closes the eye.

=M. corrugator supercilii lateralis= (Fig. 63, _d_; Fig. 64, _k_).--This consists of a number of scattered fibres which arise from among the fibres of the frontoscutularis, and from the tendon lying just craniad of the external opening of the ear, to which are united also parts of the zygomaticus (Fig. 64, _d_) and submentalis (Fig. 64, _c_). The fibres pass craniad, converging so as to form a narrow band which is inserted at the caudolateral angle of the eye, where it unites with the orbicularis oculi (Fig. 64, _s_). This muscle is continuous on the medial side with the corrugator supercilii medialis (Fig. 64, _j_) and the frontoauricularis, on the lateral side with the platysma.

_Relations._--Outer surface with the integument. Inner surface with the frontal bone and the frontoscutularis.

_Action._--Pulls the angle of the eye caudad; at the same time pulls the external ear craniad.

=M. frontoauricularis.=--A few of the fibres which are attached along the upper eyelid sometimes pass dorsocaudad, mingled with fibres of the corrugatores supercilii medialis and lateralis and the frontoscutularis, to the craniomedial angle of the auricular cartilage, where they unite with the fibres of the adductor auris superior. These fibres are sometimes distinguished as the =frontoauricularis= muscle.

=M. levator auris longus= (Fig. 63, _g_ and _g′_). (Part of the auricularis posterior of man.)--This lies on the caudal half of the dorsal surface of the head, forming a laterocaudal continuation of the intermedius scutulorum (_a_).

_Origin_ from the middle line of the neck dorsad of the atlas, and from the sagittal crest for about one centimeter craniad of the external occipital tubercle. The fibres form a broad thin sheet which passes craniolaterad as far as the caudal end of the scutiform cartilage (1). Here the muscle divides; the major portion is attached to the scutiform cartilage (1), its fibres intermingling with those of the intermedius scutulorum (_a_). The caudal portion of the muscle (_g′_) passes onto the surface of the auricle, extending one or two centimeters distad; here it is inserted on an oblique line which lies directly craniad of the insertion of the transversus auriculæ (_i_).

The caudal portion of this muscle (_g′_) having origin above the atlas and insertion on the auricle, is sometimes considered a separate muscle, the supercervicoauricular or cervicoauricular. The cranial portion (_g_) with origin on the sagittal crest and insertion on the scutiform cartilage might be distinguished as the occipitoscutularis.

The levator auris longus is continuous at its cranial end medially with M. epicranius (_h_); laterally with M. intermedius scutulorum (_a_).

_Relations._--Outer surface with the integument. Inner surface with the temporal muscle (_n_), the auricularis superior (_k_), the abductor longus auris (_m_), a narrow strand of the platysma, and the clavotrapezius.

_Action._--Pulls the external ear dorsocaudad.

The four following muscles lie partly or entirely beneath those already described; they are doubtless formed as differentiations of the inner layers of the platysma.

=M. auricularis superior= (or attollens auris) (Fig. 63, _k_).--This muscle forms a band about one centimeter broad lying just beneath the levator longus (_g_).

_Origin_ on the sagittal crest for about one centimeter craniad of the interparietal bone. The muscle passes laterad onto the surface of the auricle and is inserted into the auricular cartilage a little caudad of the middle of its convex surface. At its lateral end the cranial margin is closely united to the under surface of the levator auris longus (_g_).

_Relations._--Outer surface at the medial end with the epicranius (_h_), the abductor auris longus (_m_), and levator auris longus (_g_); at the lateral end with the skin. Inner surface with the temporal muscle (_n_) and the auricular cartilage.

_Action._--Pulls the external ear dorsad.

=M. abductor auris longus= (Fig. 63, _m_; Fig. 64, _q_). (Part of the auricularis posterior of man.)

_Origin_ on the sagittal crest dorsad of the interparietal bone, caudad of that of the auricularis superior (_k_), which it partly covers.

The muscle passes laterad as a flat band 8 to 10 millimeters wide over the caudal surface of the concha of the ear, and is inserted (Fig. 64, _q_) on the lateral surface of the eminentia conchæ, caudad of the antitragus.

_Relations._--Outer surface with the levator auris longus (_g_) and the integument. Inner surface with the auricularis superior (_k_), the abductor auris brevis (_l_), and the concha.

_Action._--Pulls the external ear caudad.

=M. abductor auris brevis= (Fig. 63, _l_).

_Origin_ by a tendon from the lambdoidal crest for one or two centimeters laterad of the middle.

The muscle passes lateroventrad lying beneath the abductor longus (_m_) as a flat band 6 to 8 millimeters wide which is inserted into the medial surface of the most proximal portion of the concha, just distad of its junction with the cartilaginous auditory meatus.

_Relations._--Outer surface with the abductor longus (_m_), a small strand of the platysma and the concha. Inner surface with the temporal muscle (_n_).

_Action._--Pulls the concha caudad.

=M. epicranius= (or occipitofrontalis) (Fig. 63, _h_ and _h′_).

_Origin_ on the sagittal crest or suture, just craniad of the origin of the levator longus auris, to the inner surface of which this muscle is closely united. From the origin the fibres pass craniad forming a band (_h_) about 8 or 10 millimeters in width, the two muscles lying close to one another and partly united in the middle line. About two centimeters craniad of their origin the fibres of both muscles end in a tendinous sheet, the =galea aponeurotica=, which covers the surface of the skull in the region between the ears and eyes, and is formed by the inner surface of the intermedius scutulorum (_a_) and other muscles of this region. The galea aponeurotica passes craniad onto the surface of the nose, where it gives origin again to a thin sheet of muscle-fibres (_h′_) which are inserted into the integument near the cranial ends of the nasal bones.

M. epicranius is thus formed of two muscular portions (_h_ and _h′_), connected by a long tendinous sheet. The caudal portion is frequently distinguished as the occipital muscle (=M. occipitalis=, _h_), the cranial portion, on the nose, as the =frontal= muscle (=M. frontalis=, _h′_).

_Relations._--Outer surface of the occipitalis (_h_) with the intermedius scutulorum (_a_), the levator auris longus (_g_), and the integument; inner surface with the auricularis superior (_h_), the abductor auris longus, and the bone. Outer surface of the frontalis (_h′_) with the integument; inner surface with the bones of the skull.

_Action._--Moves the integument of the dorsal surface of the head and of the nose.

Ventrad of the external ear the following three differentiated portions of the platysma may be distinguished.

=M. zygomaticus= (major) (Fig. 64, _d_).--A slender band connecting the angle of the mouth with the scutiform cartilage of the ear.

_a_, _a′_, _a″_, M. platysma; _b_, M. depressor conchæ; _c_, M.
submentalis; _d_, M. zygomaticus (_b_, _c_, and _d_ lie beneath the
platysma and are seen through it); _e_, M. zygomaticus minor; _f_′, M.
caninus; _f_, _g_, parts of M. quadratus labii superioris (_f_,
angular head; _g_, M. levator labii superioris alæque nasi); _h_, M.
myrtiformis; _i_, M. orbicularis oris; _j_, M. corrugator supercilii
medialis; _k_, M. corrugator supercilii lateralis; _l_, M. adductor
auris superior; _m_, M. helicis; _n_, M. antitragicus; _o_, M.
adductor auris inferior; _p_, M. conchæus externus; _q_, M. abductor
auris longus; _r_, parts of M. auricularis externus; _s_, M.
orbicularis oculi.]

At the angle of the mouth the fibres arise from among those of the orbicularis oris (_i_), from both the upper and the lower lip. They pass thence dorsocaudad across the zygomatic arch as a band 8 or 10 millimeters wide which is attached to a tendinous aponeurosis lying just craniad of the external opening of the ear. To this aponeurosis are attached also, wholly or partly, the corrugator supercilii lateralis (_k_) and the submentalis (_c_). The aponeurosis is united with the caudoventral angle of the scutiform cartilage and with the ventral edge of the cranial margin of the auricular cartilage.

This muscle is united at its cranial end with the orbicularis oris (_i_); throughout its length more or less with the platysma (_a_, _a′_); at its caudodorsal end with the corrugator supercilii lateralis (_k_) on its medial side, and with the submentalis (_c_) on its lateral side.

_Relations._--Outer surface with the integument and the platysma (_a′_). Inner surface with the masseter, temporal, frontoscutularis, and adductor auris inferior (_o_).

_Action._--Draws the angle of the mouth dorsocaudad; the external ear ventrocraniad.

=M. submentalis= (Fig. 64, _c_).--A flat band, similar to the last, and closely connected for some distance to its caudal border.

It arises as scattered fibres near the ventral middle line at about the level of the larynx, the fibres of the opposite muscles crossing the middle line and intermingling. The fibres pass dorsad, converging so as to form a narrower band, which unites dorsad with the zygomaticus (_d_), to be inserted with it into the tendinous aponeurosis above described.

_Relations._--Outer surface with the integument and platysma (_a′_). Inner surface with the muscles of the hyoid, the digastricus, the parotid gland, the masseter, the zygomatic arch and the temporal muscle.

_Action._--Draws the external ear ventrad.

=M. depressor conchæ= (Fig. 64, _b_).--A thin band of fibres, caudad of the last and parallel with it. The muscle arises as scattered fibres on the ventral surface of the neck, one or two centimeters craniad of the manubrium, the fibres of the muscles of opposite sides crossing the middle line and interdigitating. They pass dorsad, gathering together to form a narrow band which is inserted into the summit of the antitragus.

_Relations._--Outer surface with the skin at the ventral end, and with the platysma (_a′_) further dorsad. Inner surface with the deep muscles of the neck and with the parotid gland.

_Action._--Draws the external ear ventrad.

Lying deeper than the muscles thus far described, but closely connected with a number of them, are the following:

=M. frontoscutularis.=

_Origin_ (Fig. 63, _o_) on the frontal bone, along the supraorbital margin, from the craniomedial angle of the eye caudad to the zygomatic process of the frontal.

The fibres form a large muscle which passes dorsocaudad to the scutiform cartilage and is mostly attached along its ventrolateral border. Some of the outer fibres, however, pass distad of the scutiform cartilage toward the cartilage of the ear, thus joining the adductor auris superior (_f_).

The outer surface of this muscle is closely connected with fibres of the intermedius scutulorum (_a_), the corrugatores supercilii medialis (_b_) and lateralis (_d_), and the frontoauricularis, when this exists. The outer surface is covered near the origin by the orbicularis oculi (_c_), farther dorsad by the muscles just mentioned and the integument. The inner surface is in relation with the frontal bone and the adductor auris inferior (Fig. 64, _o_).

_Action._--Pulls the ear craniad.

=M. adductor auris inferior.= (Fig. 64, _o_.) (Part of the auricularis anterior of man.)--A small muscle lying beneath the frontoscutularis.