. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. EPIPTERYGOID — ALISPHENOID TRANSITION IN THERAPSIDA 41 I illustrate the structure of the primitive reptilian stock' (Romer & Price, 1940: 1), then it should not be surprising to find that this group still displays a palatoquadrate complex in which the epipterygoid and quadrate portions are linked. This condition would merely represent the retention in this group of the basic gnathostome condition of a unified palatoquadrate as exemplified in the placoderms, and retained, with modifications, in the crossopterygians
. Annals of the South African Museum. Annale van die Suid-Afrikaanse Museum. EPIPTERYGOID — ALISPHENOID TRANSITION IN THERAPSIDA 41 I illustrate the structure of the primitive reptilian stock' (Romer & Price, 1940: 1), then it should not be surprising to find that this group still displays a palatoquadrate complex in which the epipterygoid and quadrate portions are linked. This condition would merely represent the retention in this group of the basic gnathostome condition of a unified palatoquadrate as exemplified in the placoderms, and retained, with modifications, in the crossopterygians, labyrinthodonts and probably also the early stem reptiles. The epipterygoid has a wide base closely applied to the lateral surface of the anterior portion of the quadrate ramus of the pterygoid (fig. 10). Anteriorly a slender extension curves down along a groove on the dorsal surface of the palatal ramus of the pterygoid. A continuation of this groove in some cases beyond the anterior end of the bone suggests a further cartilaginous extension of the palatoquadrate. The slender rod-like portion of the epipterygoid gains contact, in Dimetrodon, with the anterior surface of the paroccipital process. EPIPTERYGOID PROOTIC QUADRATE. FOOTPLATE OF EPIPTERYGOID PTERYGOID Fig. 10. Dimetrodon limbatus. Lateral view of skull with dermal bones cut off to show palatoquadrate. (After Romer & Price, 1940.) The quadrate is essentially a triangular plate varying greatly in extent in the few forms where it is adequately known. In some cases in which it is well developed it appears to gain contact with the epipterygoid along the dorsal margin of the internal surface of the pterygoid (fig. 10), while in others in which the bone is more restricted in size, it appears to have been continued forward as cartilage. Therapsida Dinocephalia Of the slightly more advanced mammal-like reptiles, the therapsids, the Dinocephalia are generally regarded as the oldest and in many respects the most primiti
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Keywords: ., bookauthorsouthafr, bookcentury1800, bookdecade1890, bookyear1898
