22 



PBOF. D ARCY W. THOMPSON OK THE 



[Jan. 17, 



mentioned above) to bound a snpratemporal fossa. We do not 

 know whether this process is actually developed as a mere con- 

 tinuation of the prefrontal or as a posterior offshoot of the post- 

 frontal, because postfrontal and prefrontal are in all Cacatuidae 

 intimately fused ; but I am inclined to anticipate that examination 

 of vouog individuals would show it to be an outgrowth of the 

 postfrontal, and to correspond precisely to the posterior or s(jua- 

 mosal ramus of that bone in the Lacertilia. 



Fig. 12. 



Microglossus ater.rimus (reduced). 

 Fiff. 13. 



Quadrate bone of Microglossus aterrimus. 



art., the accessory articular surface beneath the jugal cup for articulation 

 with the edge of the mandible. 



The only Cockatoos in which I have observed this supratemporal 

 fossa to remain incomplete are C. ducorpsi (fig. 14) and Microglossus 

 aterrimus (fig. 12), and here we appear to have the posterior out- 

 growth or ramus of the postfrontal developed, though not to such 

 an extent as to fuse with the squamosal process. Blanchard 

 (C. E. 1856, p. 1098) says the same of Califptorhi/nchus xantho- 

 notus, but in C. banJcsi (fig. 10), which I have examined, the fossa 

 is complete and the whole region much as in other Cockatoos. 



