1032 MB. W. p. PYCBAFT ON THE [DeC. 19, 



The quadraio-jttgal extends forwards beyond the middle of the 

 quadrato-jugal bar, passing to the inner side both of the jugal and 

 maxilla. It articulates posteriorly with the quadrate, fitting into 

 a deep cup-shaped cavity. 



The vomer in the Colymbi articulates with the hemipterygoid 

 posteriorly, and with the palatine by means of its dorsal border. 



In the Podicipides, in our Museum skeleton, the relations of the 

 vomer to the hemipterygoid are not easily made out, owing to the 

 fact that the hemipterygoid has not yet split off from the pterygoid 

 (p. 1026). 



The palatine is of great length, extending forwards as a long 

 slender rod to within a short distance oF the tip of the jaw. 

 Posteriorly it is more or less grooved along its ventral aspect ; from 

 its inner dorsal border there arises caudad a leaf-like plate of bone 

 turning inwards towards the middle line, the free border of which 

 articulates with the superior border of the posterior end of the 

 vomer. 



The pterygoid, in so far as its general form is concerned, has 

 been already described. "We are concerned here only with the 

 segmentation of its anterior end to form the 



Hemipterygoid. — Tliis can best be studied in the Colymbi. Here 

 it bears a very close resemblance to that of the Impennes. In the 

 skulls of two Divers in the Museum Collection the segmentation 

 between the pterygoid and hemipterygoid is not only complete, but 

 a perfect joint has formed between the two. The hemipterygoid 

 itself has not yet fused with the palatine, but articulates with it by 

 suture. Its form is that of a short triradiate spike extending 

 forwards above the proximal end of the palatine, which underfloors 

 it, to overlap the extreme posterior end of the vomer, which, as 

 previously remarked, articulates for the most part with the palatine. 



In the Grebe, in the youngest skulls, segmentation has not yet 

 taken place ; but at the point where this is about to happen there 

 is an indication of a fracture, having jagged edges similar to that 

 figured and described recently in the Impennes, only that in tins 

 case the separation is less distinct. In a nearly adult Grebe the 

 form and relations of the hemipterygoid agree exactly with those 

 of the Diver just described. 



In the Tubinares, it will be remembered, the form of the 

 hemipterygoid differed from that just described. 



The dentary does not appear to undergo any appreciable change 

 of form between nestling and adult periods. 



The splenial is precisely similar in form, both in Grebes and 

 Divers. It resembles a flattened cone, the base contributing to 

 form the ventral border of the jaw. 



The coronoid is at first rod-shaped, then turns abruptly upwards 

 and expands into a flattened trowel-shaped blade, which remains 

 more or less distinct throughout life. 



The angidare is only just distinguishable as an independent bone. 



The supra-angulare can be distinguished as a separate hone only 

 in the youngest of the Grebes in the Museum Collection. 



