. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. EVOLUTION OF THE MAMMALIAN QUADRUPEDAL WALKING GAIT 37 strength would require an improved area of origin on the ilium and a forward development of the ilium relative to the acetabulum would enhance the pull moving the body forwards, with the hip joint as fulcrum. With the ventral adductors requiring less inward pull their area of origin in the pubo-ischiadic plate would be reduced and if shifted backwards in relation to the acetabulum contraction would have a greater propulsive component. In the vari
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. EVOLUTION OF THE MAMMALIAN QUADRUPEDAL WALKING GAIT 37 strength would require an improved area of origin on the ilium and a forward development of the ilium relative to the acetabulum would enhance the pull moving the body forwards, with the hip joint as fulcrum. With the ventral adductors requiring less inward pull their area of origin in the pubo-ischiadic plate would be reduced and if shifted backwards in relation to the acetabulum contraction would have a greater propulsive component. In the various groups of early therapsids these changes are apparent in varying degrees. Upward growth of the ilio-femoralis has pushed the axial muscles off the outer iliac surface and caused an increase in iliac Fig. 7. Femora in dorsal view, brought to the same length. a. Dimetrodon (after Romer). b. Hipposaurid. c. Pristerogna- thid. d. Anteosaurid. e. Titanosuchid. f. Tapinocephalid. g. Dicynodontid. In dromasaurs the forward growth of the ilium has been least, with the hipposaurids showing the beginning of an anterior iliac process. In the pristero- gnathids and the anteosaurs this development is only moderate, but in titano- suchids and tapinocephalids the anterior process is very well developed and in dicynodontids greatly so. In all the early therapsids the acetabulum has become rounded in outline with a strong iliac buttress, but only in dicynodontids has it moved to the anterior border. The pubo-ischiadic plate retains its great primitive length in hipposaurids, pristerognathids and anteosaurs, but in contrast to earlier forms the symphysis is strongly ossified in these groups. In titanosuchids, tapinocephalids and especially in dicynodontids the plate is greatly reduced, particularly its pubic part, and the two halves have no ossified symphysis. In these forms the backward. Please note that these images are extracted from scanned page images that may have been digital
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
