. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 32 ANNALS OF THE SOUTH AFRICAN MUSEUM affording areas of origin for the deltoid and pectoralis has remained pretty much the same and their structure is basically unchanged. Humerus (figs 2 and 3) In assuming a more upright position and in being pulled closer into the body during its backward movement, the humerus has been considerably modified and infra-ordinal differences are clearly marked. All the early therapsids have lost the strap-shaped proximal caput, which has become a long oval. In all of t
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 32 ANNALS OF THE SOUTH AFRICAN MUSEUM affording areas of origin for the deltoid and pectoralis has remained pretty much the same and their structure is basically unchanged. Humerus (figs 2 and 3) In assuming a more upright position and in being pulled closer into the body during its backward movement, the humerus has been considerably modified and infra-ordinal differences are clearly marked. All the early therapsids have lost the strap-shaped proximal caput, which has become a long oval. In all of them the caput is still terminal, but in the hipposaurids and dicynodonts it has become directed more postaxially. This is a decided advance, as with a caput in this position the humerus could swing farther backwards and thus increase the backward reach of the limb. If it is. Fig. 2. Humeri, with the distal end in dorsal view, brought to the same length, a. Dimetrodon (after Romer). b. Hipposaurid. c. Pristerognathid. d. Anteo- saurid. e. Titanosuchid. f. Tapinocephalid. g. Dicynodontid. true that the trapezius pull turned the glenoid more outwards in the dicyno- dontids then the possible forward direction of the humerus would be greater in this group than in any of its contemporaries. In the infra-orders considerable differences in this process are manifest. With a more postaxially directed caput the hipposaurids and dicynodontids could rotate the humerus on its long axis in an anti-clockwise direction (seen from the left) and this would bring the capitellum into a position facing down- ward and lying above the radius which would then be standing vertically to take the weight of the body. In the other therapsids the greater amount of untwisting of the humerus produced the same 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 perfectly res
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
