. Bulletin. Natural history. 174 PEABODY MUSEUM BULLETIN 36. FIG. 50. Diagrammatic representation of the right half of pelves of A, a pelycosaur; B, Cynogna- thus; C, a mammal, an, acetabular notch; il-ps, ilio-psoas origin; ob ex, obturator externus origin; pife, pubo-ischio-femoralis externus origin, pifi, pubo-ischio-femoralis internus origin. Not to scale. convexity on the distal end of the shaft (Fig. 54Ai-A3) but probably had a more rounded cartilaginous cap during life. There is no indication that the cartilaginous head was inflected medially or in any other direction. The articular sur
. Bulletin. Natural history. 174 PEABODY MUSEUM BULLETIN 36. FIG. 50. Diagrammatic representation of the right half of pelves of A, a pelycosaur; B, Cynogna- thus; C, a mammal, an, acetabular notch; il-ps, ilio-psoas origin; ob ex, obturator externus origin; pife, pubo-ischio-femoralis externus origin, pifi, pubo-ischio-femoralis internus origin. Not to scale. convexity on the distal end of the shaft (Fig. 54Ai-A3) but probably had a more rounded cartilaginous cap during life. There is no indication that the cartilaginous head was inflected medially or in any other direction. The articular surface as pre- served truncates the shaft transversely to the shaft axis and probably indicates that the head was a bulbous, cartilaginous cap, the center of which lay on or near to the longi- tudinal axis of the femur. Therefore the femur must have projected laterally and nearly horizontally from the pelvis. Yet femoral position cannot be accurately deter- mined from this articulation alone. The cruro-pedal articulation of pelycosaurs re- quires that the crus be directed ventrolaterally (Fig. 51 A). The femoro-crural articu- lation is composed of the proximal tibial facets that are perpendicular to the long axis of the tibia and the femoral facets that are nearly parallel to the long axis of the femur, being directed primarily ventrally but also slightly laterally. This articulation also re- quires that the crus be directed ventrolaterally, but it requires a less oblique orienta- tion (relative to the sagittal plane) than does cruro-pedal articulation. If the femur were held horizontally, the crus would be almost vertical, but then the distal end of the crus could not articulate with the pes. The solution to the apparent disparity in facet orientations requires that the distal end of the femur be slightly elevated above the proximal end (Figs. 51A; dashed line, 52B), a conclusion evidently reached by Romer (1922b: fig. 7). Compared with the pelycosaurian pattern the hip, knee an
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