PHYLOGENETIC 43 



the vomer which is of considerable width, and extends forwards 

 over the premaxillary and backwards as far as the middle of 

 the pterygoids, embracing the anterior half of each by a pair 

 of broad "feet". The palatines, it will be noticed (111. 14), are 

 short, articulating on the one hand with the vomer and pterygoid 

 where they overlap, and on the other with the maxillo-palatines, 

 which are of great size. 



The next phase of development is furnished by Rhea. The 

 vomer is here also of great size but is deeply cleft in front, 

 while the " feet " posteriorly are nearer together. Their rela- 

 tion to the vomer is precisely similar to that which obtains in 

 Dromaeus (Emu), though this fact is masked by the movement 

 of the palatines which have shifted inwards, and in so.doing have 

 come to rest under the junction between the vomer and ptery- 

 goid, concealing this when the skull is seen from the ventral 

 aspect. In their relative size and shape the palatines differ but 

 little from those of the Emu, but the maxillo-palatines are 

 relatively much wider as the palatine processes of the premaxilla 

 are also much longer. 



The palate of the Tinamous carries us a stage further. 

 The vomer is still large, and in its general conformation closely 

 resembles that of Rhea. The palatines have, however, become 

 relatively longer and rod-like ; and while posteriorly, in their 

 relation to the vomer and pterygoid, they agree with those of 

 Rhea, anteriorly they have come into touch with the palatine 

 processes of the premaxilla. The maxillo-palatines, it should 

 be noted, have become relatively smaller than in Rhea. So 

 much for these three stages in brief outline. 



Now compare any, or all three, of these palates with those 

 of, say, a Gull and a Common Fowl. For clearness' sake let 

 the comparison be made with the skull of the Fowl (111. 14). 

 One of the first things to be noted will be the greatly reduced 

 size of the vomer, which indeed is now little more than a vestige. 

 It will next be noted that this reduced vomer has lost all rela- 

 tion with the pterygoid, and is borne by an ingrowing pair of 

 plates from the palatines. These, moreover, it will be noticed, 

 have now greatly changed, both in their relative position as well 

 as in length and shape. Compared with those of Rhea and the 

 Tinamous, they will be found to have extended forwards in the 

 form of a pair of slender rods, wedged in between the palatine 



