The Skull of the Therapsida
(Figs. 43–45)
Many more modifications of the skull are found among the reptiles grouped under the name Therapsida or Anomodontia sens. lat. The supratemporals are never present. The postfrontals are often absent; the quadratojugals are present only in the Dinocephalia and are small.[1] Only in some of the Dromasauria do the lacrimals and septomaxillae exclude the maxillae from union with the nasals. There is a separate bone in front or surrounding the parietal foramen in the Anomodontia and Gorgonopsia. The parietals may be united in some of the Bauriasauria. The interparietal or dermosupraoccipital is always on the occipital surface of the bone and is unpaired; it is generally present, as also the tabulars. The temporal foramen, usually bounded above as in the Theromorpha, reaches the parietal in Therocephalia and Theriodontia, the postorbitals and squamosals not meeting. The vomers are fused into a single bone in the Gorgonopsia, Bauriasauria, and Cynodontia. The pterygoids and palatines meet in the middle line in the Dinocephalia. There is a partial false or secondary palate formed by the union of the maxillae in front of the nares in the Anomodontia, a well-formed secondary palate in the Bauriasauria and Cynodontia. The ectopterygoids may be absent or present. Only in some of the Therocephalia are there teeth on the palatal bones. The pterygoids do not meet the small quadrates in the Cynodontia. In the Cynodontia the condyle is essentially dicondylar. The parietal foramen is usually absent.
Some Dromasauria and the females of some Anomodontia are edentulous. Other anomodonts may have a single caniniform tooth in each jaw, or canines and molars. The Therocephalia have anisodont sectorial teeth, the Cynodontia with real heterodont dentition, the molars sectorial or cuspidate.
- ↑ [Broom, Sollas, Watson, and von Huene have observed a distinct quadratojugal in various Therapsida.—Ed.]
