A text-book of veterinary anatomy

The third carpal bone (Os carpale tertium, os magnum) is much the largest bone of the lower row, forming more than two-thirds of the width of the latter. It is flattened from above downward, and is twice as wide in front as behind. The superior or proximal surface consists of two facets separated by an antero-posterior ridge; the inner facet is concave and articulates with the radial carpal; the outer facet—for the intermediate carpal—is concave in front and convex behind, where it encroaches on the posterior surface. The inferior or distal surface is slightly undulating, and articulates almost entirely with the large (third) metacarpal bone, but it usually bears a small oblique facet at its inner side for the inner (second) metacarpal, and there is commonly a non-articular depression externally. The internal surface faces backward and inward, and bears three facets for articulation with the second carpal, between which it is excavated and rough. The external surface has two facets for articulation with the fourth carpal, and is depressed and rough in its middle. The anterior or dorsal surface is convex and is crossed by a rough transverse ridge. The posterior or volar surface is relatively small, and is rounded; its upper part is encroached upon by the superior articular surface, below which it is rough.

The Fourth Carpal Bone

The fourth carpal bone (Os carpale quartum, unciform) is somewhat wedge-shaped, and is readily distinguished from the second by its greater size and its posterior tubercle. The superior or proximal surface articulates with the intermediate and ulnar; it is convex and curves outward, backward, and downward, encroaching on the external and posterior surfaces. The inferior or distal surface bears two inner facets for the large (third) metacarpal and an outer one for the external (fourth) metacarpal bone. The internal surface has two or three facets for articulation with the third carpal, between which it is excavated and rough. The anterior or dorsal surface is convex and rough. The external surface is small, being encroached upon by the superior articular surface. The posterior or volar surface bears a tubercle on its lower part.^[21]

The Carpus as a Whole

The bones of the carpus, exclusive of the accessory, form an irregular quadrangular mass, the width of which is about twice the height or the antero-posterior diameter. The anterior or dorsal surface is convex from side to side, depressed along the line of junction of the two rows, and prominent below. The posterior or volar surface is in general slightly convex, but very irregular. It forms with the accessory the carpal groove (Sulcus carpi), which in the recent state is rendered smooth by the posterior ligament; it is converted into the carpal canal (Canalis carpi) for the flexor tendons by the transverse carpal ligament, which stretches across from the accessory bone to the inner side. The proximal surface is widest internally and is elevated in front, concave behind; it is entirely articular and adapted to the carpal articular surface of the radius. The distal surface is also articular and is irregularly faceted in adaptation to the surfaces of the metacarpal bones; each of the lower bones usually articulates with two metacarpal bones, but sometimes the third does not bear on the inner metacarpal bone. The lateral surfaces are both irregular and rough, the internal one being the wider. With the exception of the accessory, ulnar, and second, each bone articulates with two bones of the other row.

Development.—Each ossifies from a single center.

Three metacarpal bones (Ossa metacarpalia) are present in the horse. Of these, only one, the third or large metacarpal bone, is fully developed and carries a digit; the other two, the second and fourth, are much reduced, and are commonly called the internal and external small metacarpal or “splint” bones.

The Large Metacarpal Bone

This (Os metacarpale tertium) is a very strong long bone, placed vertically between the carpus above and the first phalanx below. It consists of a shaft and two extremities.

The shaft (Corpus) is semicylindrical, and presents two surfaces and two borders. The anterior or dorsal surface is smooth, convex from side to side, and nearly straight in its length. The posterior or volar surface is somewhat convex from side to side and, with the small bones, forms a wide groove which lodges the suspensory ligament. On either side of its upper two-thirds it is roughened for the attachment of the small metacarpal bones. The nutrient foramen occurs at the junction of the upper and middle thirds. The lower third is wider and flattened. The borders are rounded.

The proximal extremity (Basis) bears an undulating articular surface adapted to the lower row of carpal bones. The greater part supports the third carpal bone; the oblique outer part, separated from the preceding by a ridge, articulates with the fourth, and a small facet for the second is usually found at the postero-internal angle. On either side is a notch separating two small facets which articulate with the proximal ends of the small metacarpal bones. Toward the inner side of the anterior surface is the metacarpal tuberosity, into which the extensor carpi radialis is inserted. The posterior surface is roughened for the attachment of the suspensory ligament.

The distal extremity (Trochlea s. Capitulum) presents an articular surface for the first phalanx and the proximal sesamoid bones, which is composed of two condyles, separated by a sagittal ridge; the inner condyle is slightly the larger. On either side is a small fossa, surmounted by a tubercle, for the attachment of the lateral ligaments of the fetlock joint.

The large metacarpal is one of the strongest bones in the skeleton. The compact substance is specially thick in front and internally. The medullary canal extends further toward the ends than in most of the long bones of the horse and there is little spongy bone.

The Small Metacarpal Bones

These are situated on either side of the posterior surface of the large metacarpal bone, and form the sides of the metacarpal groove. Each consists of a shaft and two extremities.

The shaft (Corpus) is three-sided and tapers to the distal end. It is variably curved, convex toward the middle line of the limb. The anterior surface is flattened and is rough, except in its lower part; it is attached to the large metacarpal bone by an interosseous ligament, except near the distal end. The abaxial surface is smooth and rounded from side to side above, grooved below. The axial surface is smooth and concave from edge to edge, except below, where it forms a rounded edge.

The proximal extremity or head (Basis) is relatively large. In the case of the inner bone it usually bears two facets above which support the second and third carpal bones, while the outer bone has here a single facet for articulation with the fourth carpal bone. Each has also two facets for articulation with the large metacarpal, and is elsewhere roughened for the attachment of ligaments and muscles. The inner bone may present a small facet behind for the first carpal bone.

The distal extremity (Capitulum) is usually a small nodule, which projects to a variable extent in different subjects, and is easily felt in the living animal. It is situated two-thirds to three-fourths of the way down the region.

The small metacarpal bones vary much in length, thickness, and curvature. In the majority of cases the inner bone is the longer; in other subjects the outer one is the longer or there is no material difference. Sometimes the curvature is very pronounced, so that the distal end causes a decided projection. The distal end is very variable in size and may be a mere point.

Development.—The large metacarpal bone ossifies from three centers. The proximal extremity unites with the shaft before birth, the distal extremity toward the middle of the second year. The small metacarpal bones ossify from two centers, one of which is for the proximal extremity. Their distal ends are cartilaginous at birth. Fusion of the middle part of the shaft with the large metacarpal bone is common.

THE PHALANGES

The First Phalanx

The first phalanx (Phalanx prima)^[22] is a long bone, situated between the large metacarpal bone above and the second phalanx below. It is directed obliquely downward and forward, forming an angle of 50 to 55 degrees with the horizontal plane in well-formed limbs. It consists of a shaft and two extremities.

The shaft (Corpus) is wider and much thicker above than below, and presents two surfaces and two borders. The anterior or dorsal surface is convex from side to side and smooth. The posterior or volar surface is flattened, and bears a triangular rough area, bounded laterally by ridges which begin at the tuberosities above and converge below; this area furnishes attachment to the inferior sesamoidean ligaments. The borders, internal and external, are rounded and have a rough area or a tubercle on their middle parts.

The proximal extremity (Basis) is relatively large. It bears an articular surface adapted to the distal end of the large metacarpal bone, consisting of two glenoid cavities separated by a sagittal groove; the inner cavity is a little larger than the outer one. The posterior angles are formed by buttress-like tuberosities for ligamentous attachment. The anterior surface has a slight elevation for the attachment of the lateral extensor tendon.

The distal extremity is smaller, especially in its antero-posterior diameter. It presents a trochlea for articulation with the second phalanx, consisting of a shallow central groove and two lateral convex areas or condyles; the inner area is a little the larger. On either side, just above the margin of the articular surface, is a depression surmounted by a tubercle, to both of which the lateral ligament is attached. Behind the tubercle is a distinct facet to which the superficial flexor tendon is attached.

Development. The first phalanx ossifies from three centers. The distal end unites with the shaft before birth, the proximal end early in the first year.

The first phalanx contains a small medullary canal in the middle of the shaft. It may be remarked that the bone is twisted slightly; when placed volar surface down on the table, it touches the latter by three points only, the proximal tuberosities and the internal condyle.

The Second Phalanx

The second phalanx (Phalanx secunda)^[23] is situated between the first and third phalanges, its direction corresponding to that of the first phalanx. It is flattened from before backward, and its width is greater than its height. It may be described as possessing four surfaces.

The upper or proximal surface presents two glenoid cavities separated by a low ridge, and articulates with the first phalanx. The middle of the anterior border is elevated and roughened in front for the attachment of the anterior or common extensor tendon. The posterior border is thick and overhanging; in the fresh state its middle part is covered with cartilage, over which the deep flexor tendon passes. On either side there is an eminence, to which the lateral ligament and the superficial flexor tendon are attached.

The inferior or distal surface is trochlear, and articulates with the third phalanx and third sesamoid bone. It resembles somewhat the trochlea of the first phalanx, but is more extensive and encroaches more on the anterior and posterior surfaces.

The anterior or dorsal surface is convex from side to side and smooth in its middle; on its lower part are lateral rough depressions, surmounted by tuberosities, to both of which ligaments are attached.

The posterior or volar surface is smooth, flattened, and slopes obliquely downward and forward. The borders which separate the anterior and posterior surfaces are concave from above downward, rounded from before backward.

Development.—The second phalanx ossifies like the first, but the proximal end unites with the shaft two or three months earlier.

The Third Phalanx

The third or ungual phalanx (Phalanx tertia)^[24] is entirely inclosed by the hoof, to which it conforms in a general way. It presents for examination three surfaces, three borders, and two angles or wings.

The articular surface (Facies articularis) faces upward and backward, and is chiefly adapted to the distal surface of the second phalanx, but a narrow flattened area along the posterior border articulates with the third sesamoid. The anterior or coronary border forms a central eminence, the extensor (or pyramidal) process (Processus extensorius), to the front of which the anterior extensor tendon is attached. On either side is a depression for the attachment of the lateral ligament.

The dorsal or wall surface (Facies dorsalis) slopes downward and forward. The angle of inclination on the ground plane is about 45 to 50 degrees in front. Laterally the height diminishes, and the slope becomes steeper, especially on the inner side. From side to side the curvature is almost semicircular. The surface is rough and porous, resembling pumice stone somewhat. It is perforated by numerous foramina of various sizes; a series of larger ones is situated on or near the lower border. On either side the dorsal (or preplantar) groove (Sulcus dorsalis) passes forward from the wing and ends at one of the larger foramina. In the fresh state this surface is covered by the matrix of the wall of the hoof. The inferior or distal border is thin, sharp, and irregularly notched; there is commonly a wider notch in front.

The volar or inferior surface (Facies volaris) is arched, and divided into two unequal parts by a curved rough line, the semilunar crest (Crista semilunaris). The larger anterior area is crescent-shaped, concave, and comparatively smooth; it corresponds to the sole of the hoof, and may be termed the sole surface. The posterior part is much smaller, and is semilunar; it is related to the deep flexor tendon, and is hence called the flexor or tendon surface (Facies flexoria). It presents a central prominent rough area, on either side of which is the volar (or plantar) foramen (Foramen volare), to which the volar (or plantar) groove (Sulcus volaris) conducts from the wing. The foramina lead into the semilunar canal within the bone, from which small canals lead to some of the foramina of the wall surface. The deep flexor tendon is inserted into the semilunar crest and the central rough area behind it.

The volar grooves and foramina transmit the terminations of the digital arteries into the semilunar canal, where they meet and form a terminal arch, from which branches pass through canals in the bone and emerge through the foramina on the wall surface.

The angles or wings (Anguli) are prismatic masses which project backward on either side; the inner one is usually the shorter. Each is divided into upper and lower parts by a notch, or is perforated by a foramen which leads to the vascular groove on the side of the wall surface.^[25] The upper border carries the lateral cartilage.

The lateral cartilages (Cartilagines ungulæ) are rhomboid curved plates, which surmount the wings on either side. They are relatively large and extend above the margin of the hoof sufficiently to be distinctly palpable. The abaxial surface is convex, the axial concave. The upper border is convex and thin; the lower is thicker and is in part attached to the wing. The anterior end is attached by ligament to the side of the second phalanx. The posterior end curves toward its fellow at the heel, and is perforated by numerous foramina for the passage of veins. The central part is mainly hyaline, the periphery mainly fibrous.

It will be noted that the size and form of the wings vary much in different specimens. In the new-born foal the wing is a small, pointed projection. Later the process of ossification invades the lower part of the cartilage to a varying extent. In some cases the greater part of the cartilage is ossified—a condition commonly termed “sidebone.”

Development.—The ossification of the terminal phalanx is peculiar. While the proximal articular part is still cartilaginous, a perichondrial cap of bone is formed in relation to the hoof. Later the process extends into the upper part.

Structure.—The interior of this bone is channeled by numerous canals for vessels, most of which radiate from the semilunar canal to the wall surface; these are not canals for nutrient vessels of the bone, but transmit arteries to the matrix of the hoof. Thick layers of compact substance are found at the articular and flexor surfaces and the extensor process, i. e., at the points of greatest pressure and traction.

THE SESAMOID BONES

The two proximal or great sesamoids (Ossa sesamoidea phalangis primæ) are situated behind the distal end of the large metacarpal bone, and are closely attached to the first phalanx by strong ligaments. Each has the form of a three-sided pyramid. The anterior or articular surface conforms to the corresponding part of the distal end of the large metacarpal bone. The posterior or flexor surface is flattened and oblique; in the fresh state it is covered by a layer of cartilage which also fills the interval between the opposed borders of the two bones, and forms a smooth groove for the deep flexor tendon. The abaxial surface is concave, and gives attachment to part of the suspensory ligament; it is separated from the posterior surface by a rough everted border. The base faces downward, and furnishes attachment to the inferior sesamoidean ligaments. The apex is directed upward and is rounded.

The third sesamoid or navicular bone (Os sesamoideum phalangis tertiæ) is shuttle-shaped, and is situated behind the junction of the second and third phalanges. Its long axis is transverse, and it possesses two surfaces, two borders, and two extremities. The articular surface (Facies articularis) faces upward and forward; it consists of a central eminence, flanked by concave areas, and articulates with the distal end of the second phalanx. The flexor or tendon surface (Facies flexoria) is directed downward and backward. It resembles the articular surface in form, but is more extensive and not so smooth. In the fresh state it is coated with cartilage and the deep flexor tendon plays over it. The proximal border (Margo liber) is wide and grooved in its middle, narrower and rounded on either side. The distal border (Margo ligamenti) bears in front a narrow facet for articulation with the third phalanx. Behind this is a groove, which contains a number of relatively large foramina, and is bounded behind by a prominent edge. The extremities are blunt-pointed.

Development.—It ossifies from a single center.

The Bones of the Pelvic Limb

The pelvic girdle consists of the ossa coxæ, which unite ventrally at the symphysis pelvis, and articulate with the sacrum dorsally.

OS COXÆ

The os coxæ (or os innominatum) forms the skeleton of the hip or haunch, and is the largest of the flat bones. It consists primarily of three parts, the ilium, ischium, and pubis, which meet to form the acetabulum, a large cotyloid cavity for articulation with the head of the femur. These parts are fused at about one year of age, but it is convenient to describe them separately.

The ilium (Os ilium) is the largest of the three parts. It is irregularly triangular and presents two surfaces, three borders, and three angles.

The gluteal surface (Facies glutæa) faces upward, backward, and outward. It is wide and concave in front, narrower and convex behind. The wide part is crossed by the curved gluteal line (Linea glutæa), which extends from the middle of the inner border toward the external angle. This surface gives attachment to the middle and deep gluteal muscles.

The pelvic surface (Facies pelvina) faces in the opposite direction; it is convex, and consists of two distinct parts. The inner triangular part (Pars articularis) is roughened for ligamentous attachment, and bears an irregular facet, the auricular surface (Facies auricularis), for articulation with the sacrum. The outer quadrilateral part (Pars iliaca) is in general smooth. It is crossed by the ilio-pectineal line (Crista iliopectinea), which begins below the auricular surface and is continued on the shaft of the bone to join the anterior border of the pubis. The line is interrupted by furrows for the iliaco-femoral vessels, and below these it bears the psoas tubercle (Tuberculum psoadicum), which gives attachment to the psoas minor muscle. The iliacus muscle is attached to the surface external to the ilio-pectineal line.

The anterior border or crest (Crista iliaca) is concave, thick, and rough.

The internal border is deeply concave; its middle part forms the lower boundary of the great sciatic foramen, and it is continuous behind with the superior ischiatic spine.

The external border is concave and in great part rough. Its fore part is crossed by grooves for the ilio-lumbar vessels, which are continued on the pelvic surface. The nutrient foramen is usually situated on or near the posterior part of this border.

The internal or sacral angle (Tuber sacrale) curves upward and a little backward close to the first sacral spine, and forms here the highest point of the skeleton. It is somewhat thickened and rough.

The external or coxal angle (Tuber coxæ) forms the basis of the point of the hip. It is a large quadrangular mass, narrow in its middle, and enlarged at either end, where it bears a pair of tuberosities. It is roughened for muscular attachment.

The posterior or acetabular angle meets the other two bones at the acetabulum, of which it forms about two-fifths. Its prominent upper border forms part of the superior ischiatic spine, which is roughened externally, smooth internally. Two depressions above and in front of the acetabulum give attachment to the tendons of origin of the rectus femoris muscle. This angle is connected with the ala or wide part of the bone by a constricted part, often termed the shaft. The latter is of three-sided prismatic form. Its external surface is convex and rough, and gives attachment to the deep gluteus muscle. Its pelvic surface is smooth and is grooved for the obturator vessels and nerves. Its ventral surface is crossed by vascular grooves, below which is a rough area, bounded internally by the psoas tubercle.

THE ISCHIUM

The ischium (Os ischii) forms the posterior part of the ventral wall or floor of the bony pelvis. It slopes a little downward and inward, but is practically horizontal in the longitudinal direction. It is irregularly quadrilateral, and may be described as having two surfaces, four borders, and four angles.

The superior or pelvic surface (Facies pelvina) is smooth and slightly concave from side to side.

The inferior surface (Facies externa) is nearly flat, and is in great part roughened for the attachment of the adductor muscles.

The anterior border forms the posterior margin of the obturator foramen.

The posterior border is thick and rough. It slopes obliquely inward and forward to meet the border of the other side, forming with it the ischial arch (Arcus ischiadicus).

The internal border meets the opposite bone at the symphysis.

The external border is thick and rounded, but concave in its length; it forms the lesser sciatic notch, the lower boundary of the lesser sciatic foramen.

The antero-internal angle or symphyseal branch (Ramus symphyseos) meets the pubis, with which it forms the inner boundary of the obturator foramen.

The antero-external angle or acetabular branch joins the other two bones at the acetabulum, of which it forms more than half. Superiorly it bears part of the superior ischiatic spine (Spina ischiadica), and internally it is grooved for the obturator vessels.

The postero-external angle is a thick three-sided mass, the tuber ischii (Tuber ischiadicum); its lower border is the inferior ischiatic spine, to which the biceps femoris and semitendinosus muscles are attached.

THE PUBIS

The pubis (Os pubis) is the smallest of the three parts of the os coxæ. It forms the anterior part of the pelvic floor, and may be described as having two surfaces, three borders, and three angles.

The superior or pelvic surface (Facies pelvina) is convex in the young subject and the stallion, concave and smooth in the mare and usually in the gelding also. The urinary bladder rests on it.

The inferior or ventral surface (Facies externa) is convex, and in great part rough for muscular attachment. Near the anterior border it is crossed by the subpubic groove, the inner part of which is occupied by a large vein, the outer part by the pubo-femoral ligament.

The anterior border is thin in its inner part (except in the young subject and the stallion), forming the pecten ossis pubis. Externally it bears the rough ilio-pectineal eminence (Eminentia iliopectinea), beyond which it is continuous with the ilio-pectineal line.

The internal border joins the opposite bone at the symphysis pubis.

The posterior border forms the anterior margin of the obturator foramen, and is marked externally by the obturator groove.

The internal angle meets its fellow at the anterior end of the symphysis. This part is very thick in the young subject and the stallion, but in the mare, and usually in the gelding also, it becomes thin with advancing age.

The external or acetabular angle joins the ilium and ischium at the acetabulum.

The posterior angle joins the ischium, with which it forms the inner boundary of the obturator foramen.

The pubis may conveniently be regarded as consisting of two branches which meet at a right angle; these are termed the transverse or acetabular branch (Ramus acetabularis) and the longitudinal or symphyseal branch (Ramus symphysecs).

The acetabulum is a cotyloid cavity which lodges the head of the femur. It faces downward and outward, and consists of an articular and a non-articular part. The articular part (Facies lunata) is crescentic, and is cut into internally by the non-articular part, which lies at a lower level, and is termed the acetabular fossa (Fossa acetabuli). The inner part of the rim is correspondingly cut into by the acetabular notch (Incisura acetabuli), which is converted into a foramen by the transverse ligament in the fresh state, and transmits the pubo-femoral and round ligaments to the head of the femur.

The obturator foramen (Foramen obturatum) is situated between the pubis and ischium. It is oval in outline, the longer axis being directed forward and outward. Its margin is grooved antero-externally for the obturator nerve and vessels.

Development.—Each division of the os coxæ ossifies from one chief center. The center for the ilium appears first near the acetabulum, followed quickly by one for the ischium, and a little later by the pubic center. Secondary centers appear for the crest and external angle of the ilium, the tuber and posterior border of the ischium, and the acetabular part of the pubis. The pubis and ischium are united at birth or soon after, but are not fused with the ilium until the second year. The epiphyseal parts fuse with the main mass at four and a half to five years of age.

The acetabular part of the pubis ossifies from a separate center. It is most distinct in the embryo at three months, and is often called the os acetabuli. Martin says that the ilium has a center for the acetabular part, one for the shaft and wing, and a third for the crest. He also states that there is a special center for the acetabular part of the ischium, and a transitory nucleus in the symphyseal part of the pubis.

THE PELVIS

The bony pelvis is composed of the ossa coxarum, the sacrum, and the first three coccygeal vertebræ. The dorsal wall or roof is formed by the sacrum and first three coccygeal vertebræ, and the ventral wall or floor by the pubic and ischial bones. The lateral walls are formed by the ilia and the acetabular part of the ischia. The defect in the skeleton here is supplied in the fresh state by the sacro-sciatic ligaments and semimembranosus muscles.

The anterior aperture or inlet (Apertura pelvis cranialis) is bounded by the terminal line (Linea terminalis) or brim, composed of the base of the sacrum dorsally, the ilio-pectineal lines laterally, and the anterior border of the pubis ventrally. It is almost circular in the mare, semi-elliptical in the stallion, and faces obliquely downward and forward. It has two principal diameters. Of these, the conjugate or sacro-pubic diameter (Conjugata) is measured from the sacral promontory to the anterior end of the symphysis. The transverse diameter (Diameter transversa) is measured at the greatest width, i. e., just above the psoas tubercle.

The posterior aperture or outlet (Apertura pelvis caudalis) is much smaller and is very incomplete in the skeleton. It is bounded above by the third coccygeal vertebra and below by the ischial arch; in the fresh state it is completed laterally by the sacro-sciatic ligament and the semimembranosus muscle.

The axis of the pelvis is an imaginary line drawn through the centers of the inlet, cavity, and outlet.

Sexual Differences.—Marked differences exist in the size and form of the pelvis in the two sexes. The average conjugate diameter is about 9½ inches (ca. 23 to 24 cm.) in the mare, 7½ inches (ca. 18 to 20 cm.) in the stallion. The transverse diameter of the inlet averages about 9 inches (ca. 22 to 23 cm.) in the mare, and 8 inches (ca. 20 cm.) in the stallion. The obliquity of the inlet is greater in the female; the difference is indicated by the fact that a vertical plane from the pecten cuts the fourth sacral segment in the female, the second in the male. The outlet is also larger in the mare, the ischial arch being about one-third wider than in the stallion. The cavity is much more roomy in the female; the transverse diameter between the middles of the superior ischiatic spines is about 8 inches (20 cm.) in the mare, 6 inches (15 cm.) in the stallion. The pubic part of the floor in the female is concave and lies considerably lower than the ischiatic part, which is wide and relatively flat. In the stallion the pubis is very thick centrally, and this part of the floor is convex, while the ischial part is relatively narrow, and is concave from side to side. The obturator foramina are correspondingly larger in the female. The ilium is shorter, and the greater sciatic notch deeper and narrower in the male. The pelvis of the gelding, when castration has been performed early, resembles that of the mare; otherwise the male characters appear to be retained to a large degree.

THE FEMUR

The femur or thigh bone (Os femoris) is the largest and most massive of the long bones. It extends obliquely downward and forward, articulating with the acetabulum above and the tibia and patella below. It presents for examination a shaft and two extremities.

The shaft or body (Corpus femoris) is in general cylindrical, but flattened behind, and larger above than below. The anterior and lateral surfaces are continuous and strongly convex from side to side; there is often a central vertical rough line on the proximal part, but otherwise these surfaces are smooth. They are covered by the quadriceps femoris muscle. The posterior surface is wide, flat, and smooth in its proximal fourth. Below this part there is a rough elevation externally for the attachment of the femoral tendon of the biceps femoris, and a rough line internally to which the quadratus femoris is attached. The middle third is narrower, and is rough for the attachment of the adductor muscle. Just below this area an oblique groove crosses the surface, indicating the position of the femoral vessels. The internal border bears on its proximal part the internal trochanter or trochanter minor, a thick rough ridge, to which the ilio-psoas muscle is attached. From this a rough line curves up to the front of the neck and indicates the limit of the attachment of the vastus internus muscle. A narrow rough area about the middle gives attachment to the pectineus muscle, and the nutrient foramen is usually found just in front of this mark. The supracondyloid crest is situated below the groove for the femoral vessels, and gives origin to the inner head of the gastrocnemius. The external border is prominent in its upper part, and bears at the junction of its proximal and middle thirds the external or third trochanter (Trochanter tertius); this process is curved forward, and furnishes insertion to the tendon of the superficial gluteus muscle. At the lower part is found the supracondyloid or plantar fossa (Fossa plantaris), in which the superficial flexor arises; it is bounded externally by a thick rough margin, to which the outer head of the gastrocnemius muscle is attached.

The proximal extremity (Extremitas proximalis) is large and consists of the head, neck, and great trochanter. The head (Caput femoris) is placed at the inner side and is directed inward, upward, and somewhat forward. It is approximately hemispherical and articulates with the acetabulum. It is cut into internally by a deep notch, the fovea capitis, in which the pubo-femoral and round ligaments are attached. The articular surface is surrounded by a distinct margin. The neck (Collum femoris) is most distinct in front and internally. The great trochanter (Trochanter major) is situated externally; it presents three features. The anterior part or convexity is situated opposite to the head and rises little above the level of the latter; it gives attachment to the deep gluteus muscle, and in the fresh state its outer surface is coated with cartilage, over which a tendon of the middle gluteus passes, to be inserted into the crest, which is placed below and behind the convexity. The posterior part or summit is separated from the convexity by a notch; it is situated behind the plane of the head and rises to a much greater height. It furnishes insertion to part of the middle gluteus muscle. Its posterior border is continued downward as the trochanteric ridge, which forms the outer wall of the trochanteric fossa. A number of foramina are found in the concave area internal to the convexity.