(Canis familiaris) × ½.
A femur, B tibia, C fibula, D patella.
| 1. head of femur. | 5. external condyle. |
| 2. neck. | 6. internal condyle. |
| 3. great trochanter. | 7. fabella. |
| 4. shaft. | 8. cnemial crest. |
The pubis (fig. 78, 12) is smaller than either the ischium or ilium; it does not take part in the formation of the acetabulum, and like the ischium, meets its fellow in a ventral symphysis. The acetabular bone (fig, 78, B, 14) is small and triangular, and is wedged in between the other three. It forms about one-sixth of the acetabulum.
The Posterior Limb.
The posterior limb, like the anterior, is divisible into three parts; these are the thigh, the crus or shin, and the pes.
The thigh contains only a single bone, the femur.
The femur is a long straight bone with a nearly smooth shaft and expanded ends. The proximal end bears on its inner side the large rounded head (fig. 79, A, 1) which articulates with the acetabulum. External to the head and divided from it by a deep pit is a large rough outgrowth, the great trochanter (fig. 79, 3). The deep pit is the trochanteric or digital fossa. On the inner side below the head is a smaller roughened surface, the lesser trochanter. The lower or distal end of the bone bears two prominent rounded surfaces, the condyles, which articulate with the tibia. They are separated from one another by the deep intercondylar notch, which is continued above and in front as a shallow groove, lodging a large sesamoid bone, the patella or knee-cap. At the back of the knee-joint are a pair of smaller sesamoids, the fabellae (fig. 79, 7).
In the young animal there are three epiphyses to the shaft of the femur, one forming the head, one the great trochanter, and one the distal end.
The crus or shin contains two bones, the tibia and fibula. The tibia is a fairly thick straight bone, expanded at both ends, especially at the head or proximal end. The proximal end is triangular in cross section, and bears two facets for articulation with the condyles of the femur. The anterior surface of the proximal end of the tibia is marked by the strong cnemial crest (fig. 79, 8), which runs some way down the shaft. The distal end of the tibia articulates with the astragalus by an irregular, somewhat square surface.