1905.] OSTEOLOGY OF THE EURYL^EMID-E. 51 



formes. A further indication of specialisation is the fact tliat 

 the squamosal, in all the Passeriformes and most of the Coracii- 

 formes, has absorbed the underlying bones so that it now 

 appears, almost in its entirety, within the cranial cavity. The 

 remai'kable variations which obtain in the Class Aves, in the form 

 and arxungement of the membrane-bones are of considerable 

 interest. These changes seem to follow along certain definite 

 lines, and are the more remarkable because, save for the first few 

 weeks of the bird's life (the nestling period in short), these bones, 

 as separate entities, cease to exist, being fused to form one 

 homogeneous tissue. Yet progressive evolution is as obvious as in, 

 say, the sternum oi- pelvis ; though they cannot be individually 

 influenced by the strains and stresses incident to the struggle for 

 existence in the same way as if they maintained their individuality 

 throughout life, or for at least some considerable time after leaving 

 the nest. This is a point to which I propose to return later. 



So far we have described only the specialised features of the 

 skull ; what of the primitive ? It is difficult to speak with any 

 degree of certainty on this point. The small size of the 

 anterior, posterior, and superior tympanic recesses, and of the 

 tympanic cavity, may be reckoned in this category ; and so too, 

 probably, should the long narrow vomer as seen in Galyptoniena. 

 The close approximation of the otic and squamosal heads of the 

 cjuadra,te is an undoubtedly primitive chai-acter. These, in the 

 E'lrylsemidte, are barely separated ; in the Corvidas, for example, 

 they are comparatively wide apart. These few points seem to sum 

 ap all the evidence that is obtainable on this question. 



How far specialisation has gone in the skulls within this group 

 may be seen at a glance by comparing the skull of Galyptomena 

 with, say, that of Corydon. In the latter the antorbital plate is 

 greatly reduced in size and thickness, and the lachrymal is 

 wanting. The beak is markedly wider, more hooked, and 

 articulates with the frontal by a more pronounced nasal hinge, 

 while the nasal sejotum is obliterated by the inflation of the nasal 

 processes of the premaxLlla. 



The simple, unforked condition of the spina externa of the 

 sternum is undoubtedly a primitive character ; and in the form 

 of the pelvic girdle this group is less advanced than in the 

 remaining Passeres. 



Before proceeding to discuss the relationship of the Eurylaemidee 

 to the remaining Passeres, it would be well to say a few words as to 

 the wider question, of the probable allies of the Euryltemidse 

 outside the Passeres. This is a matter on which it is impossible 

 to dogmatise ; at most, one can but throw out suggestions, of a 

 very nebulous character. 



It will be found, probably, that Flirbringer (3) has come nearest 

 to the solution of this problem. He points to a relationship 

 between the Euryleemida? and the Cypseli, and a yet closer alliance 

 with the Pici. Aflinities to the Coraciidce he regards as remote 

 indeed . 



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