FIG. 19. A. Skull of a Therocephalian, Lycosuchus vanderrieti ; length 

 of skull about 9 inches. B. Skull of a Theriodont, Cynognathus platy- 

 ceps ; length of skull about 9 inches. C. Skull of a Mammal, Dasyurus 

 maculatus ; length of skull about 4 inches. 



Ang., Angular ; Art., Articular ; Dent., Dentary ; Fr., Frontal ; Ju.,Jugal; 

 L., Lacrymal ; MX., Maxilla ; Na., Nasal ; Pa., Parietal ; Pmx., Pre-maxilla ; 

 P.O., Postorbital ; Pr. F., Pre-frontal ; Qu., Quadrate ; S. Ang., Surangular ; 

 Sq., Squamosal. 



In no existing mammal are the nostrils separated by bone as in the 

 Theriodonts, but in the early stages of development of the egg-laying 

 mammals of Australia the pre-maxillaries aie found with ascending median 

 processes very similar to those of fossil forms. 



