52 THE OSTEOLOGY OF THE REPTILES 



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 postf rontals are often absent ; 

 the quadratojugals are present only in the Dinocephalia and are 

 small. ^ Only in some of the Dromasauria do the lacrimals and septo- 

 maxillae 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, usu- 

 ally bounded above as in the Theromorpha, reaches the parietal in 

 theTherocephaha andTheriodontia,the postorbitals and squamosals 

 not meeting. The vomers are fused into a single bone in the Gor- 

 gonopsia, Bauriasauria, and Cynodontia. The pterygoids and pala- 

 tines 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 Therocephaha 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 Therocephaha have aniso- 

 dont sectorial teeth, the Cynodontia with real heterodont dentition, 

 the molars sectorial or cuspidate. 



1 [Broom, Sollas, Watson, and von Huene have observed a distinct quadratojugal 

 in various Therapsida. — Ed.] 



