INTRODUCTION.
In our 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
relying too implicitly on the affinities 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 being 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 imperfect
nature of our conceptions we suppose to have been created, may lead the most
trufhful 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 in that unity.
As in Mammals, the cranium with its dental armature is the part of the skeleton from
which the Palaeontologist derives the most certain indications 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 in 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 fossae, and the height of the ridges giving attachment to the muscles, of mastication,
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