PROFESSOR OWEN ON THE GENUS DINORNIS. 353 



thence the bony roof of the mouth. It is convex above, where it forms a very thin 

 shell of bone ; on the outside of this tumid part of the maxillary is the sutural surface 

 for the premaxillary and nasal bones, the latter being the smaller part. The malar 

 process of the maxillary (PI. LV. fig. 1, 21) extends backward from the outer and 

 posterior angle ; the inner angle terminates in a point, which was onderlapped by the 

 palatine. 



Neither palatines nor pterygoids are preserved in the present skull. The maxillary 

 (21), malar (26), and squamosal (27) coalesce to form the usual slender and straight 

 zygomatic arch in birds. This increases in depth and diminishes in thickness at the 

 squamosal part, which shows a feebly convex upper border : its posterior end is 

 thickened to form the convexity adapted to the cup (PI. LIII. fig. 2, h) on the outer 

 part of the tympanic (28). 



The modifications of certain parts of the skull of the Dinornis robustus are of a nature 

 to throw light on some moot points in the craniology of birds. 



Dr. Melville contends that " the interorbital septum in Birds is the homologue of the 

 Mammalian presphenoid."' But of this presphenoid in Pigeons he describes the " ossi- 

 fied portions of the ethmoid, or olfactory capsule," to be processes^. Moreover, he 

 admits that the ' interorbital septum ' appears on the upper surface of the cranium 

 "behind the premaxillary, and between the nasals," "in the Emu and other Stru- 

 thionidse."^ It is shown in this exposed position in the Ostrich (art. Aves, Cyclop, of 

 Anat. vol. i. p. 274, fig. 127, I) as part of the ' ethmoid ', in the Emu (Zool. Trans, 

 vol. iii. pi. 39. figs. 1 & 2, 14) as ' prefrontals,' and in the Rhea (Zool. Trans, vol. v. 

 pi. 42) as the ' middle ethmoid ' or ' perpendicular ethmoid.' 



I have not, however, met with any instance, in any class, in which the • anterior 

 sphenoid ' afforded attachment to ' turbinals ' or ossified parts of the olfactory capsule. 

 Anthropotomists describe and figure the homologue of the ' presphenoid ' as the 

 " ' rostrum '* of the sphenoid bone, to which is articulated the vomer and the perpen- 

 dicular part of the ethmoid." 



The ' rostral ' form and proportions of the ' anterior sphenoid ' in Cetacea approach 

 nearer to those of the ' rostrum of the sphenoid ' in Birds and Reptiles than in most 

 other mammals. I am unable, therefore, to accept the special homology of the ' inter- 

 orbital septum' in birds proposed or adopted by Dr. Melville. His views of the 

 " general homology " of the part in question are expressed as follows : — " For reasons 

 which cannot be discussed here, I regard the interorbital septum as the compressed 

 body of the third and last or most anterior of the cranial vertebrae."^ But, in this 

 case, we have the hody or centrum of a vertebra appearing at the upper surface of a 

 neural arch, and displacing the moieties of a neural spine, projecting, e. g., " between 

 the nasals," as in the Struthious birds already adduced. And beneath this part so 



' " Dodo and its Kindred," 'Osteology of the Dodo,' -Ito, 1848, p. 87. ' Ibid. ' Ibid. 



' 'Anatomy, Descriptive aud Surgical,' by H. Gray, 8vo, p. 33, fig. 30. ' Op. cit. p. 87. 



VOL. v. PART V. 3 A 



