514 



note is concerned are the articular, the pre-articular, angular and 

 tfurangular. 



The articular expands posteriorly and has a saddle-shaped sur- 

 face, facing upwards and backwards to receive the quadrate. The 

 close resemblance between this bone and the malleus in the foetus, 

 assuming the manubrium to be secondary, seems too striking to leave 

 any room for doubt as to the homology of the two bones. 



The quadrate of the Cynodont is not figured, but its shape agrees 

 generally with that of the incus. 



Fig. 3. Fig. 4. 



Fig. 3. External view of posterior part of lower jaw in the Cynodont. 

 ang. angular ; art. articular ; dent, dentary. 



Fig. 4. Internal view of same. Lettering a§ Fig. 3. 

 ^.arf. . pre-articular. s.ang. surangular. 



Watson has described a peculiar feature of the therapsid jaw, 

 in which the angular bone is invariably more or less deeply notched, 

 the development of the notch in the more specialised forms produ- 

 cing a forked condition. From the obvious correspondence in position 

 and shape of this bone in the Cynodont to the tympanic in the foetal 

 Perameles, it seems clear that the mammalian tympanic bone is the 

 modified angular of the Eeptiles. 



This view has been suggested but not demonstrated by Broom, 



