Part 9

=The Wrist.=--At the wrist or carpus there are in reality three joints, the first between the radius and ulna proximad and the first row of carpals distad, the second between the two rows of carpal bones, the third between the distal row of carpals and the metacarpals. The first two are movable joints; the third is not. Each of these three joints has a capsule, and the bones entering into the joints are interconnected by numerous ligaments. These ligaments are named by combining the names of the two bones which they interconnect. Ligaments which interconnect bones of the same row in the carpus are sometimes distinguished as =interosseous= ligaments, as contrasted with =intercarpal= ligaments, which connect together bones of different rows. According to their position the ligaments may also be distinguished as dorsal, ventral, and lateral. Detailed descriptions and figures of all these ligaments are given by Strauss-Durckheim.

=Metacarpals.=--The joint between the carpals and metacarpals has been described. At the distal end of the metacarpals the articulations with the phalanges have each a capsule. The joint is further strengthened by a double lateral ligament on each side. The two sesamoid bones at each joint are interconnected by a strong transverse ligament, and each is connected with the head of the metacarpal and the base of the first phalanx by a lateral ligament.

=Phalanges.=--Between the phalanges the joints possess capsules, and each has a radial and an ulnar lateral ligament.

VI. BONES OF THE PELVIC EXTREMITIES.

=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.

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_).

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.

=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.

=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.

_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.