Bones of the Pelvic Limb

The ilium is nearly parallel with the median plane and its axis is only slightly oblique with regard to the horizontal plane. The gluteal surface is concave. The iliac surface is almost flat. The auricular surface faces almost directly inward, and in front of it there is an extensive rough area. The ilio-pectineal line is very distinct and is uninterrupted. The anterior border or crest is strongly convex, thick, and rough. The internal angle is represented by a thickened part which bears two eminences, homologous with the posterior superior and posterior inferior iliac spines of man. The external angle also has two prominences, which are equivalent to the two anterior spines present in man. The shaft is almost sagittal and is compressed laterally. Above it is smooth and rounded, and below it bears a crest externally which terminates at a tuberosity in front of the acetabulum.

The ischium has a twisted appearance owing to the fact that its acetabular part is nearly sagittal while the posterior part is almost horizontal. The two bones also diverge behind and the tubera are flattened and everted. The superior ischiatic spine is low and thick; its posterior part is marked by transverse grooves and has a prominent outer lip. There is no lesser sciatic notch. The ischial arch is relatively small and is semi-elliptical.

The symphyseal part of the pubis is thick and fuses late with the opposite bone. There is no subpubic groove.

The acetabulum is about twice as far from the external angle of the ilium as from the tuber ischii. The fossa acetabuli is deep, and is bounded internally by a flat plate of bone; its floor is so thin as to be translucent. There is a small notch behind.

The obturator foramen resembles in outline an equilateral triangle with the angles rounded off.

The inlet of the pelvis is very oblique. It is almost circular in the female, but in the male it is elliptical and the conjugate diameter is the longer. The cavity is narrowest between the acetabula, and very wide behind. The floor is concave and relatively narrow in front, wide and flat behind.

The femur is relatively much longer than in the horse or ox. The shaft is regularly cylindrical, except near the extremities, where it is wider and compressed from before backward. It is strongly curved in its lower two-thirds, convex in front. The posterior surface is flattened transversely, narrow in the middle, and widens toward each end. It is bounded by two rough lines (Labium laterale, mediale) which diverge toward the extremities. The third trochanter and the plantar (supracondyloid) fossa are absent. There are two supracondyloid crests, the inner one being small. The nutrient foramen is in the upper third of the posterior surface. The head is a little more than a hemisphere and has a shallow depression behind and external to its center. The neck is well defined. The trochanter major does not extend as high as the head; a thick ridge runs from its anterior surface to the neck. The internal trochanter has the form of a blunt tuberosity. The trochanteric fossa is round and deep. The ridges of the trochlea are practically sagittal in direction and are almost similar. The intercondyloid fossa is wide. Just above each condyle posteriorly there is a facet for articulation with the sesamoid (of Vesal), which is developed in the origin of the gastrocnemius muscle.

The tibia is about the same length as the femur. The shaft forms a double curve; the upper part is convex internally, the lower part externally. The proximal third is prismatic, but is compressed laterally and is long from before backward. The remainder is almost regularly cylindrical. The crest is short but very prominent. The nutrient foramen is usually in the upper third of the external border. The tuberosity is not grooved, but bears a distinct mark where the ligamentum patellæ is attached. There is a small facet for the fibula on the postero-external part of the external condyle, and a small sesamoid bone in the tendon of origin of the popliteus is in contact with the posterior angle of the latter. The distal end is quadrangular and relatively small. The articular grooves and ridge are almost sagittal. There is a facet externally for articulation with the fibula. There is a vertical groove internally and a shallower one behind—both for tendons.

The fibula extends the entire length of the region. It is slender, somewhat twisted, and enlarged at either end. The upper part of the shaft is separated from the tibia by a considerable interosseous space, but the lower part is flattened and closely applied to the tibia. The proximal end is flattened and articulates with the external condyle of the tibia. The distal end is somewhat thicker and forms the external malleolus. It articulates internally with the tibia and the tibial tarsal bone. Externally it bears two tubercles.

The patella is long and narrow. The anterior surface is convex in both directions. The articular surface is convex from side to side and slightly concave from above downward.

The tarsus comprises seven bones. The tibial tarsal consists of a body, neck, and head, like the bone in man. The body presents a trochlea above for articulation with the tibia and fibula. The posterior surface has three facets for articulation with the fibular tarsal bone. The head is directed a little inward and articulates with the central. The fibular tarsal has a long anterior process or “beak,” but the inner process (sustentaculum) is short. The tuber calcis is grooved from before backward. The central has a concave proximal surface adapted to the head of the tibial tarsal. Its distal surface articulates with the first, second, and third tarsals. It bears two tubercles posteriorly. The first tarsal is flattened and irregularly quadrangular; it articulates above with the central and below with the first metatarsal. The second tarsal is the smallest and is wedge-shaped; it articulates below with the second metatarsal bone. The third tarsal is also wedge-shaped, the base being in front; it articulates with the third metatarsal below. The fourth tarsal is remarkably high, and resembles a quadrangular prism; it articulates with the fibular tarsal above, the fourth and fifth metatarsal below, and the central and third tarsal bones internally. A groove for the tendon of the peroneus longus crosses its outer and posterior surface, and above it are one or two tubercles.

Five metatarsal bones are present. The first is commonly very small and has the form of a blunt cone, somewhat compressed laterally. It articulates with the first tarsal and furnishes insertion to the tibialis anterior muscle. In some cases it fuses with the first tarsal; when the first digit is well developed, its metatarsal may resemble the others (except in size) or be reduced in its proximal part to a fibrous band. The other metatarsals are a little longer than the corresponding metacarpals. Their proximal ends are elongated from before backward and have posterior projections, which in the case of the third and fourth usually bear facets for articulation with two small rounded sesamoid bones. In other respects they resemble the metacarpals.

The first digit is often absent. When present, its development varies and it contains one or two phalanges. In other cases the digit is double. The phalanges of the other digits resemble those of the fore limb.