PHYLOGENY OF THE PAL.EOGNATH.E AND NEOGNATH^E. 205 



pterygoid above and the palatine below. A portion of this flange-like plate of the 

 palatine helps to fill up the cleft between the pterygoid fork already described. As 

 mentioned above, the palatine rests upon a backwardly directed plate from the maxillo- 

 palatine process, the whole of which it conceals from the dorsal aspect. Ventrally, 

 this process is found to run along, and below, the external palatine border, and to 

 terminate near its extreme posterior end. The forward extension of the palatine on 

 the ventral surface corresponds with the level of the tip of the vomer. This extension 

 is derived from the ventral surface-layers of the main body, the palatine terminating 

 abruptly on the dorsal aspect in a V-shaped notch at the level of the middle of the 

 vomer. This ventral process rests in a groove along the mesial border of the maxillo- 

 palatine process. 



The relations of the vomer have already been more or less indicated. Suffice it to 

 say, that the free end of each posterior limb is wedged in between the spine-like 

 extremity of the pterygoid above and the flange-like inward projection from the dorsal 

 surface of the palatine below. 



The palate of Apteryx will be found, on a close comparison with that of the remaining 

 Palceognathoe, to have departed from the typical Struthious form in the direction of 

 that taken by Rhea, the relations between palatine and vomer being similar in both. 

 The form of the pterygoid differs from that of all other birds, in that ic is bifid, or, in 

 that it sends off a separate limb whose mesial border passes downwards to underlie the 

 external border of the palatine. This external, palatine limb is elsewhere unrepre- 

 sented. The internal, vomerine limb may be regarded as a flattened plate folded upon 

 itself, the edge being inwards. The superior edge, or upper lip, must be regarded as 

 representing the mesial border of an originally flattened pterygoid such as that of 

 Dromceus. 



The dentary is of great length. In Dromceus, Casuarius, Rhea, Apteryx, and 

 Tinamous it extends backwards to within one-fourth of the whole length of the ramus. 

 It is relatively less in Struthio. Caudad each ramus divides into dorsal and ventral 

 limbs, of which the ventral is the larger. In Rhea the dorsal limb is paired. 



The splenial is of great length in all, extending forwards to the symphysis of the 

 jaw, and backwards to within a short distance of the level of the glenoid cavity for the 

 quadrate. It is rod-like in Struthio, laterally compressed in the remaining forms. 



The angular, in all save Apteryx, articulates, proximally, with the supra-angular, 

 being embedded caudad in its external border ; distally, it twists downwards so as to 

 form the ventral border of the ramus. In Casuarius and Dromceus its extreme posterior 

 and inner border comes into contact with the articular. In Rhea and Struthio, it falls 

 considerably short of this. 



In Apteryx, the angular articulates proximally with the ventral border of the 

 articular, which is hollowed out to receive it. The supra-angular rests upon its 

 dorsal border. 



vol. xv. — part v. No. 13. — December, 1900. 2 Q 



