The ilium is a somewhat cylindrical bone which at its ventral end meets the ischium, and forms part of the acetabulum. It is then directed upwards and slightly backwards, and is attached to the ribs of the sacral vertebra.
The ischia are a pair of somewhat square bones which meet one another in the middle line; they form part of the acetabulum, and are united to the ilia above.
In front of the ischia is a narrow cartilaginous area which represents the pubes. Projecting forwards from it is a bifid cartilaginous epipubis.
D. The Posterior limb.
This is divisible into a proximal portion, the thigh, a middle portion, the crus or shin, and a distal portion, the pes.
The thigh consists of a single bone, the femur (fig. 23, A, 1), which has a thin shaft and expanded ends. The anterior part of the pre-axial border and posterior part of the postaxial border bear slight outgrowths.
The crus or shin includes two short bones, the tibia and fibula, which are nearly equal in length. The pre-axial bone or tibia is a straight bone thickest at its proximal end, the postaxial bone or fibula (fig. 23, A, 3) is a rather stouter curved bone of nearly equal diameter throughout.
The pes includes the tarsus or ankle, and the foot.
The tarsus consists of eight small bones arranged in a proximal row of three, the tibiale, intermedium and fibulare, and a distal row of four tarsalia, with one bone, the centrale (fig. 23, A, 7), interposed between the two rows. In the specimen examined, the tibiale, is a small bone articulating with the tibia, the intermedium (fig. 23, A, 5) is larger and articulates with both tibia and fibula, the fibulare is the largest of the three and articulates with the fibula.
The bones of the distal row are tarsalia 1, 2, 3, and a bone representing 4 and 5 fused. In the specimen examined tarsale 1 is pushed away dorsally (fig. 23, A, 8), so as to lie between the tibiale and tarsale 2. All the tarsal bones are small and somewhat polygonal, and are connected with one another, and with the tibia and fibula on the one hand, and with the metatarsals on the other by a thin layer of cartilage.