This extraordinary Bird (fig.
182) appears to have been about as big as a Rook--the tail being
long and extremely slender, and composed of separate vertebrae,
each of which supports a single pair of quill-feathers. In the
flying Birds of the present day, as before mentioned, the terminal
vertebrae of the tail are amalgamated to form a single bone
("ploughshare-bone"), which supports a cluster of tail-feathers;
and the tail itself is short. In the embryos of existing Birds
the tail is long, and is made up of separate vertebrae, and the
same character is observed in many existing Reptiles. The tail
of _Archoeopteryx_, therefore, is to be regarded as the permanent
retention of an embryonic type of structure, or as an approximation
to the characters of the Reptiles. Another remarkable point in
connection with _Archoeopteryx_, in which it differs from all
known Birds, is, that the wing was furnished with two free claws.
From the presence of feathers, _Archoeopteryx_ may be inferred to
have been hot-blooded; and this character, taken along with the
structure of the skeleton of the wing, may be held as sufficient
to justify its being considered as belonging to the class of
Birds. In the structure of the tail, however, it is singularly
Reptilian; and there is reason to believe that its jaws were
furnished with teeth sunk in distinct sockets, as is the case
in no existing Bird.
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