For instance,

viviparous quadrupeds have all a head and a neck,
and all the parts or organs of the head, but they differ each from
other in the shapes of the parts. The lion has its neck composed of
one single bone instead of vertebrae; but, when dissected, the
animal is found in all internal characters to resemble the dog.

The quadrupedal vivipara instead of arms have forelegs. This is
true of all quadrupeds, but such of them as have toes have,
practically speaking, organs analogous to hands; at all events, they
use these fore-limbs for many purposes as hands. And they have the
limbs on the left-hand side less distinct from those on the right than
man.