PHYLOGENY OP THE PAL.EOGNATIUE AND NEOGNATH^. 185 



of the orbito-nasal nerve, accompanying it to its tip, so as to bring the sense of smell 

 to aid the sense of touch found in the Ibises. 



It is interesting to note that in the very early embryo, as shown in Parker's figures, 

 the position of the external nares is near the middle of the beak. Its forward shifting 

 seems to be involved in the growth of the elongating beak. 



The Maxillo-jugal Arch. 



The maxilla in Casuarius takes the form of an elongated flattened splint. Its 

 interior. half has the outer and inner borders turned upwards to meet in the mid-dorsal 

 line so as to form a long thin-walled tunnel tapering forwards to a point. This is the 

 antrum. The rim of the mouth of this is produced backwards into two short spikes; 

 the outer forms a strong dorso-lateral and the inner a lateral spike, conspicuous when the 

 skull is viewed ventrally. The floor of this tunnel, viewed ventrally, is twice as wide as 

 the posterior region of the maxilla. This wider region — the floor of the antrum, — 

 which in the ventral view presents a deeply hollowed free posterior border forming the 

 anterior boundary of the posterior narial aperture, is the maxillo-palatine process. 



The whole inner border of this process is grooved for the reception of the vomer. 

 The maxilla extends forwards above the maxillary and palatine processes of the pre- 

 maxilla. The latter process is received into a shallow depression in the maxillo- 

 palatine, a raised ridge of which bone can be seen lying between the palatine and 

 maxillary process. The backward extension of the maxilla is considerable. It runs 

 below the quadrato-jugal bar on the outer side and the palatine on its inner side to a 

 point slightly beyond the level of the free border of the hinder end of the posterior 

 nares, or, to take another standard, to within a short distance of the base of the vomer. 



The quadrato-jugal fossa is the name which I have applied to indicate the large 

 space enclosed by the quadrato-jugal bar on the outside, the palatine and pterygoid in 

 the inside, and the hinder end of the maxilla in front. 



In Casuarius it does not extend forwards beyond the hinder end of the posterior 

 narial aperture. 



In Dromceus the maxilla is relatively much wider than in Casuarius, and does not 

 extend so far backwards. The maxillo-palatine processes are wider but very much 

 shorter antero-posteriorly than in Casuarius. The antrum, in consequence, is much 

 reduced in length and capacity. Its dorsal wall, moreover, is fenestrated. The mesial 

 borders of the maxillo-palatine processes rest upon the vomer. 



The quadrato-jugal fossa extends forwards to within a short distance of the middle 

 of the posterior narial aperture. 



In Dinornithidce the maxillo-palatine region of the maxilla is short and broad. Its 

 anterior end is wedged in between the maxillary and palatine processes of the pre- 

 maxilla. Ventrally it appears as an oblong flattened plate. Its postero-internal 

 border bounds the anterior end of the posterior nares. Its posterior border is either 

 notched or hollowed and forms the anterior boundary of the quadrato-jugal fossa. 



