The =ilium= (figs. 58 and 61, 1) is the largest bone of the pelvis. It forms a long flattened plate extending for a considerable distance both in front of and behind the acetabulum, and is fused along its whole length with the transverse processes and neural spines of the sacral and pseudosacral vertebrae. It forms more than half the acetabulum, above and behind which it is produced to form a process, the =antitrochanter= (fig 61, 8), with which the great trochanter of the femur articulates. [Illustration FIG. 61. LATERAL VIEW OF THE PELVIS AND SACRUM OF A DUCK (_Anas boschas_) × 2/3. 1. ilium. 2. ischium. 3. pubis. 4. pectineal process. 5. acetabulum. 6. ilio-sciatic foramen. 7. fused vertebrae. 8. antitrochanter.] The =ischium= (figs. 58 and 61, 2) is a flattened bone which forms about one-third of the acetabulum, and lies ventral to the posterior part of the ilium. Its anterior portion is separated from the ilium by the large oval =ilio-sciatic foramen= (fig. 61, 6), while behind this the two bones are completely fused. The =pubis= (figs. 58 and 61, 3) is a very long slender bar of bone which forms only a very small part of the acetabulum and runs back parallel to the ventral surface of the ischium with which it is loosely connected at its posterior end. For the greater part of their length the two bones are separated by the long narrow =obturator foramen=. Behind the ischium the pubis is produced into a long curved downwardly-projecting process, and in front of the acetabulum it bears a short blunt =pectineal= or =pre-pubic process= (fig. 61, 4) probably homologous with the pre-pubis of Orthopod Dinosaurs. The remainder of the pubis is homologous with the post-pubis of Orthopod Dinosaurs. THE POSTERIOR LIMB. The leg of the bird is somewhat differently constructed from that of other vertebrates owing to the fact that there is no free tarsus, the proximal tarsals having fused with the tibia, and the distal with the metatarsals. The =thigh= consists of a single bone, the femur. The =femur= is a comparatively short bone with a straight shaft and expanded ends. The proximal end bears on its inner side a rounded =head=, which articulates with the acetabulum. On its outer side is an irregular outgrowth, the =great trochanter=, while between the two is the surface which meets the antitrochanter of the ilium. The posterior end also is expanded and marked by a wide groove which lodges the =patella=. On each side of the groove is a strong =condylar ridge= for articulation with the tibia. The external condyle is deeply grooved behind for articulation with the fibula. The =crus= or =shin= consists of two separate bones, (1) the =tibio-tarsus=, formed by the fusion of the tibia with the proximal row of tarsals, and (2) the =fibula=.