in the three bones of a toe, the last of which is encased in the hoof of
the hind-foot. Now turn to the Dog's skeleton. We find identically the
same bones, but more of them, there being more toes in each foot, and
hence more toe-bones.

Well, that is a very curious thing! The fact is that the Dog and the
Horse--when one gets a look at them without the outward impediments of
the skin--are found to be made in very much the same sort of fashion.
And if I were to make a transverse section of the Dog, I should find the
same organs that I have already shown you as forming parts of the Horse.
Well, here is another skeleton--that of a kind of Lemur--you see he has
just the same bones; and if I were to make a transverse section of it,
it would be just the same again. In your mind's eye turn him round, so
as to put his backbone in a position inclined obliquely upwards and
forwards, just as in the next three diagrams, which represent the
skeletons of an Orang, a Chimpanzee, a Gorilla, and you find you have no
trouble in identifying the bones throughout; and lastly turn to the end
of the series, the diagram representing a man's skeleton, and still you
find no great structural feature essentially altered. There are the same
bones in the same relations. From the Horse we pass on and on, with
gradual steps, until we arrive at last at the highest known forms. On
the other hand, take the other line of diagrams, and pass from the Horse
downwards in the scale to this fish; and still, though the modifications
are vastly greater, the essential framework of the organization remains
unchanged. Here, for instance, is a Porpoise: here is its strong
backbone, with the cavity running through it, which contains the spinal
cord; here are the ribs, here the shoulder blade; here is the little
short upper-arm bone, here are the two forearm bones, the wrist-bone,
and the finger-bones.