ANCESTRY OF THE MAMMALIA 



49 



unlike the mammalian condition is the separation of the nostrils 

 from each other in Bauria not by cartilage only but by an up- 

 wardly directed process of the premaxilla such as occurs in 

 Amphibians. Birds and many other Reptiles. Another ele- 

 ment in the skull of the Cynodont not usually found in Mam- 

 mals although occurring in certain forms which have retained 



Fig. 10. — Side view of restored skull of Bauria cynops. (After Broom.) Abbrevia- 

 tions as in Fig. 8, A. Fi\, frontal; Ju., zygoma; La., lachrymal; Mx., maxilla; Xa., 

 nasal; Pa., parietal; Pmx., premaxilla; PoO., postortital; Smx., septomaxillary. 



very primitive features (Ornithorhynchus, Echidna, Dasypus) 

 is the septomaxillary which in Bauria appears on the face 

 between the nasal and the premaxilla but as we shall see 

 later becomes partly submerged in Sesamodon and retires into 

 the nose itself. In the undifferentiated condition of the pre- 



Fig. 11. — Side view of restored skull of Sesamodon browni. (After Broom.) Ab- 

 breviations as in Figs. 8-A and 10. Aud. Gr., groove for lodgment for external auditorv 

 canal. 



molar-molar series, the absence of a complete postorbital arch, 

 the large frontals and the condition of the septomaxillary Bau- 

 ria approaches more closely than Sesamodon to the probable 

 mammalian ancestor. 



