1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS, 435 



and ill Didus it is nearly at right angles to the ramus of the mandible. 

 The form of the angle of the mandible in Dicluncuhis is quite unlike 

 that observed in the other Columbidce and in Didus. In these re- 

 spects, therefore, Didunculus departs further from the ordinary Co- 

 lumbidce than the Dodo does. 



1 am indebted to Mr. E. Higgins for a skin of that singular 

 bird Opisthocomus cristatus, from which I was able to extract an 

 imperfect skull, the inferior face of which is represented in fig. 1 7. 

 The base of the cranium and the pterygoid bones are wanting. 

 The underside of the unossified nasal septum supports tlie slender 

 vomer {Vo), which expands and becomes bifurcated anteriorly, in 

 a manner unlike anything which I am acquainted vvith in other 

 birds*. The very slender anterior processes of the palatine boues 



Fig. 17. 



\ 



Opisthocomus cristatus. 

 Under view of an imperfect skull. The letters as before. 



(the bodies of which are almost entirely wanting in this specimen) 

 are overlapped by the short and broad maxillo-palatines, which 

 remain very distant from the vomer and from one another. The 

 angle of the mandible is slightly produced and bent upwards. 



These are all the birds (leaving the Cracidtje aside) in which I 

 have noticed the Schizognathous disposition of the palate, which, 

 it must be observed, is characterized not only by the complete di- 

 stinctness of the maxillo-palatines from one another and from the 

 vomer, but by the slender and usually pointed form of the latter bone. 



III. Those Cuvierian Grallse and Natatores which are not Schi- 

 zognathous, the Accipitres or Raptores, the Scansores, and, among 

 the Passeres, most of the Fissirostres, all the Syndactyli, and Upiqia 

 may be termed Desmognathous. 



In these birds the vomer is often either abortive, or so small that 

 it disappears from the skeleton. When it exists it is always slender 

 and tapers to a point anteriorly. 



* In some of the Falcons the vomer has a nearly similar anterior termination, 

 but its connexions are different. 



