1905. | OSTEOLOGY OF THE EURYLEH MIDE, 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, mm 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 
mee are barely separated ; in the Corvide, 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 Cor ydon. In the latter the antorbital plate is 
oveatly 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 Hurylemid 
to the remaining Passeres, it would be well to saya few words as to 
the wider question, of the probable allies of the Hurylemide 
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 Fiirbringer (3) has come nearest 
to the solution of this problem. He points to a relationship 
between the Hurylemide and the Cypseli, and a yet closer alliance 
with the Pici. Affinities to the Coraciidse he regards as remote 
indeed. 
A* 
