INTRODUCTION. 
In ovr efforts to determine the affinities of an extinct or fossil bird, by comparison of its 
osseous remains with the same parts in existing forms, we must be on our guard against 
relymg too implicitly on the atlinities which appear to be indicated by an incidental 
similarity in absolute: size of the things compared, overlooking the more important elements 
for guiding us to a correct conclusion, namely, correspondence of general form and minute 
configuration. 
Having obtained an approximate idea of the affinities by a comparison rightly instituted, 
we should next enquire whether the existing species of the type to which it has been referred 
afford a range in the form and relative proportions of important homologous parts, sufficiently 
wide to allow of its anomalies bemg admitted within the limits of the probable variations 
of the type. 
The too frequent disposition to discern in each newly-acquired form, recent or extinct, 
one of those links between now dissevered groups of animated beings, which, from the im- 
perfect nature of our conceptions we suppose to have been created, may lead the most 
truthful observer into error in determining its proper rank. The progress of discovery has 
indeed added members to some apparently defective families, but all attempts to fuse great 
conterminous groups together, have only more clearly illustrated the fundamental unity of 
organization, without destroying the multiplicity im that unity. 
As in Mammals, the cranium with its dental armature is the part of the skeleton from 
which the Palzontologist derives the most certain mdications as to the position of an extinct 
species ; so in Birds, the same segment of the osseous frame-work is that which preserves the 
typical characters, notwithstanding such alterations m other parts as may even annihilate 
the power of flight, that almost universal characteristic of the class. The variations in the 
number, size, and pattern of the teeth in Mammals, denoting essential differences in the 
nature of the food selected, are parallelled in birds by modifications in the form, size and 
relative proportions of the beak, and its horny sheath. , 
The force and extent of the movements of the mandibles have an essential relation to 
the nature of the food, and the resistance to be overcome in its prehension. Hence the depth 
of the muscular fossee, and the height of the ridges giving attachment to the muscles of masti- 
cation, cannot but convey to us valuable information, which should further be correlated with 
that resulting from the indications of the amount of movement of the head on the trunk. 
The form of the palatine bone especially deserves attention, from its giving attachment to one 
