1902.] OSTEOLOGY OF THE FALCONIFORMES. 285 



aliethmoidal extensions of this plate extend backwards so as 

 to form a complete olfactory chamber leading backwards du'ectly, 

 tunnel- wise, into the brain-cavity, through the apertures for the 

 olfactory nerve. 



In the Tubinai'es we have a very similar olfactoiy chamber, 

 but of far greater size. This is due to the fact that the prefrontal, 

 which is enormous, aiises so far back that the interorbital septum 

 is reduced to a small ring of bone suii-ounding the interorbital 

 fenestra. Fui'thermoi-e, the backward position of the prefrontal 

 has involved it in the formation of the lower lateral segment of 

 the apei'tui-e foi- the olfactoiy nerve, which may also be legitimately 

 described as enormous. The uppei- lateral segment of this circular 

 aperture is formed by the downturned edge of the horizontal 

 aliethmoidal plate. Normally, in Neognathfe, the olfactory nerve 

 leaves by a small foiumen pierced through the free edge of the 

 oi'bital plate of the frontal and the perpendicular plate of the mes- 

 ethmoid, runs in a groove along the doi'sal border of the plate, 

 and thence gains the olfactory chamber. In the instance we 

 have just examined, the olfactory aperture opens directly into the 

 chamber. 



It is possible that the conditions which obtain in the Tubinares 

 may represent a primitive stage, the olfactoiy chamber having 

 been pushed forwards by the great development of the orbits, 

 demanded by the increasing size of the eye. In xijyteryx, where 

 the eyes are very small, the olfactory cavity is in close juxta- 

 position with the brain-case. The fact that the chamber is of still 

 greater relative size, and very complicated intei'iially, only indicates 

 a further specialization of the primitive condition. In the Palfeo- 

 gnatha3 we may trace several stages in the forward shifting of 

 the olfactory chamber coirelated with increased size of the eyes 

 and orbits; as a study of the skulls of Dinornis, Struthio, 

 Dromceus, Rhea, and Tinamus will show. 



The development of the olfactoiy cavity is a point which will 

 evidently repay further investigation. 



The nasal septum is divided by a considerable gap, or cleft, 

 from the mesethmoid. This cleft, the cranio-facial fissure, is widest 

 venti'ally ; the mesethmoid and nasal septum being in contact 

 immediately below the nasal processes of the premaxilla. In the 

 Oathartfe alone among the Falconiformes, the external nares ai-e 

 pervious, only the proximal portion of the nasal septum being 

 present. This, in Pseudogryphus califomiamis, extends forwards 

 for a short distance to encroach upon the external narial aperture, 

 and is pierced by a round fenestra. This posterior portion of the 

 nasal septum, in Cathartse, expands to form a broad base which, 

 extending outwards on either side, joins the widely separated 

 maxillo-palatine processes, and so converts a schizo- into an in- 

 directly desmognathous palate. In many of the true Vultures, 

 e. g. Gyps, by the ossification of the alinasal ectoethmoidal wall, 

 the nostril, in the dried skull, is of the same shape as in life. 

 The olfactory region of the nasal labyrinth, in Gy2')s, is provided 



