ologous with, for example, the
uncinate processes of the ribs in birds (see Figs. 5 and 6). The
fore-limb is a simple filament in _Lepidosiren_, and presents few joints
in _Proteus_ and _Amphiuma_; in other air-breathing Vertebrates it shows
a more complete development, the humerus, radius and ulna, and the bones
of the wrist and hand becoming differentiated out.

As the fore-limb is equivalent to a single bone of the archetype, it is
said to be, in its developed state, "teleologically compound" (p. 103).

Since in the archetype every vertebra has its appendage, more than two
pairs of locomotory limbs might have been developed. "Any given
appendage might have been the seat of such developments as convert that
of the pelvic arch into a locomotive limb; and the true insight into the
general homology of limbs leads us to recognise many potential pairs in
the typical endoskeleton. The possible and conceivable modifications of
the vertebrate archetype are far from having been exhausted in the forms
which have hitherto been recognised, from the primaeval fishes of the
palaeozoic ocean of this planet up to the present time" (p. 102). It is
not of the essence of the vertebrate type to be tetrapodal.

In determining homologies Owen remained true to Geoffroy's principle of
connections. Speaking of an attempt which had been made to determine
homologies by the mode of development, he writes, "There exists
doubtless a close general resemblance in the mode of development of
homologous parts; but this is subject to modification, like the forms,
proportions, functions, and very substance of such parts, without their
essential homological relationships being thereby obliterated. These
relationships are mainly, if not wholly, determined by the relative
position and connection of the parts, and may exist independently of
form, proportions, substance, function and similarity of development.
But the connections must be sought for at every period of development,
and the changes of relative position, if any, during growth, must be
compared with the connections which the part presents in the classes
where vegetative repetition is greatest and adaptive modification least"
(p. 6). It is interesting to note that in Owen's opinion comparative
anatomy explains embryology. Thus the scapula, which is the
pleurapophysis of the occipital vertebra, is vertical on its first
appearance in the embryo of tetrapoda, and lies close up to the head
(_On the N