284 MR. W. p. PYCEAFT ON THE [Apr. 15, 



The interorhital septum is pierced only in the lower members of 

 the various groups of Falconiformes. For instance, in Serpentarius 

 and Cathartes, in Panclion and Fernis, Polyhorides, Gypohierax^ 

 and the lower Vultures and Eagles. 



The Ethimoidal Region. — The meseihmoid, as in Neognathse 

 generally, is, as it were, obliquely truncated at its anterior end, 

 so that its free edge slopes upwards and forwards. This is due 

 probably to the shortening of the par-asphenoidal rostrum. This 

 shortening process is very conspicuous in the Accipitres. It 

 rarely, if ever, extends f oi-wards beyond the level of the lachrymals 

 in any Neognathfe. In the Palseognathfe this rostrum extends 

 forwards for a considerable distance in front of a line drawn 

 transversely throiigh the skull across the lachrymals. The 

 mesethmoid extends backwards, as in all other birds, to fuse with 

 the orbital plate of the frontal, and the orbito- and presphenoid, 

 and the parasphenoidal rostrum below ; thus forming the inter- 

 orbital septum referred to above. From the neighbourhood of 

 its truncated anterior border springs, on either side, a more or 

 less extensive wing-like process — the j»;re/ro?itoZ or antorbital 

 plate. 



The 2^'>'^fi'ontcd is somewhat feebly developed in Serpentarius, 

 Folyboroides, and Pernis, for instance. In Cathartre and in the 

 Falcons it is much larger ; in the latter it extends outwards to 

 afford a more or less extensive lateral support for the lachrjanal. 

 In the former, the lachrymal and prefrontal relations become still 

 more intimate, since they fuse one with another. 



The 2^'>'&orhital region of the mesethmoid expands dorsad into 

 a broad horizontal plate underlying the anterior ends of the 

 frontals, the nasals and the nasal processes of the premaxillary. 

 In the Vultures, Eagles, and Cathartte markedly, and in the 

 majority of the Accipitres to a less extent, the free edges of 

 the horizontal aliethmoidal plate turn downwards and inwards, 

 and finally backwards, to join the prefrontal ; thus forming an 

 ossified olfactory chamber. This is most perfectly developed in 

 the Catharta^, where the chamber is of very considerable extent, 

 recalling that of the Tubinares. In Serpentarius, the Falconidse, 

 and Buteonidfe, this ossified olfactory chamber is extremely 

 reduced. In the two latter forms perhaps the great development 

 of the prefrontal may be regarded as filling the place of the 

 ossifications of the horizontal plate. 



The olfactory nerve, in leaving the skull, generally travels along 

 a groove in the dorsal border of that poi'tion of the mesethmoid 

 which forms the interorhital septum ; sometimes this groove is 

 covered in by the ossification of connective tissvxe, e. g. Oathartae. 



I would revert once again to the comparison between the 

 olfactoiy chamber of Cathai'tte and that of the Tubinares. In 

 the former the free edge of the horizontal aliethmoidal plate 

 turns downwards on either side mesiad of the. lachrymal, so as to 

 leave a considerable space between itself and the lachiymal, to 

 form the Harderian fossa. Furthermore, it would seem that the 



