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Show 1905.] OSTEOLOGY OF THE EURYLAEMIDAE. 51 formes. A further indication of specialisation is the fact that 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 remarkable variations which obtain in the Class Aves, in the form and arrangement 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 or 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 Calyptomena. The close approximation of the otic and squamosal heads of the quadrate is an undoubtedly primitive character. These, in the Eurylaemidie, are barely separated ; in the Corvidae, for example, they are comparatively wide apart. These few points seem to sum up 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 Calyptomena 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 septum is obliterated by the inflation of the nasal processes of the premaxilla. 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 Eurylaemidae to the remaining Passeres, it would be well to say a few words as to the wider question, of the probable allies of the Eurylaemidae outside the Passeres. This is a matter 011 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 Fiirbringer (3) has come nearest to the solution of this problem. He points to a relationship between the Eurylaemidae and the Cypseli, and a yet closer alliance with the Pici. Affinities to the Coraciidre he regards as remote indeed. 4* |