. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. SKELETON OF AN EARLY DICYNODONT 219 cartilage would be necessary to achieve this. In a sprawling position the dorsally-facing head comes into contact with the ventrally-facing dorsal margin of the acetabulum. Also, the condyles on the femur for articulation with the tibia and fibula are ventrally-facing, suggesting that the crus was at right angles to the femur, in turn implying that this was perpendicular to the acetabulum. The muscle configuration of the hind limb (Fig. 7B, F-G) would seem to suppo
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. SKELETON OF AN EARLY DICYNODONT 219 cartilage would be necessary to achieve this. In a sprawling position the dorsally-facing head comes into contact with the ventrally-facing dorsal margin of the acetabulum. Also, the condyles on the femur for articulation with the tibia and fibula are ventrally-facing, suggesting that the crus was at right angles to the femur, in turn implying that this was perpendicular to the acetabulum. The muscle configuration of the hind limb (Fig. 7B, F-G) would seem to support this conclusion, since, judging from their areas of attachment, muscles such as the pubo-ischio-femoralis externus, ventral adductor, femorotibialis and gastrocnemius were all well developed. The former two muscles would certainly have had a postural function. The latter two, although concerned with flexing the limb, would also have been important posturally. However, the position of the head on the anteromedial extremity of the femur does suggest in-turning of the bone implicated in the change from a sprawling to a more erect limb position. If the femur of Robertia is compared with that of a pelycosaur such as Dimetrodon, however, it can be seen that the head of Robertia is not so much in-turned but rather that the posteromedial part of the articulatory surface has been reduced (Fig. 11). Also, the articulatory surface of the femur of Robertia has become more rounded and bulbous and concentrated on the dorsal side. The obvious consequence of these changes in a sprawling-gaited animal would be to allow a longer protraction-retraction arc before the posterior margin of the femur touched the border of the acetabulum and before contact of the femur head and the acetabulum was lost. In particular, B. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not
Size: 1408px × 1775px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
