1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 441 



direct bony union, with the two maxillo-palatines, which are some- 

 times scroll-shaped, sometimes greatly swollen and spongy. 



The vomer, sometimes slender, sometimes pretty broad, always 

 tapers to a point anteriorly. 



The basipterygoids sometimes are and sometimes are not present. 



The angle of the mandible is not produced and recurved. 



Four modifications of the general type of palatine structure are 

 observable among the Raptorial birds : — 



In the genera Cathartes and Sarcorhamphus the cleft between the 

 thin and scroll-like maxillo-palatines is very deep and wide, and the 

 ossification of the septum is small in extent, and only forms a sort 

 of bridge over the deep and wide valley between the maxillo- 

 palatines. 



The basipterygoid processes are large and articulate with the 

 pterygoids (fig. 22). 



In all the Owls the maxillo-palatines are thick and spongy, and 

 encroach upon the intermediate valley, though they never com- 

 pletely unite with one another across it or obliterate its upper part. 

 The basipterygoid processes are always present (fig. 23). 



Fig. 23. 



Pmr 



The base of the skull of Otus vulgaris. 



The letters have the same signification as before. The inferior and internal 

 margins of the spongy maxillo-palatines almost come into contact ; but their 

 inner faces are separated by a wide interval. * The prefrontal processes. 

 The basipterygoid processes are not marked. 



In the Secretary bird {Gypogermius) the maxillo-palatines unite 

 with one another and with the extensively ossified septum, so as 

 to fill up the maxillo-palatine valley. There are well-developed 

 basipterygoid processes. 



