his organs of sense are the same in number and occupy
the same relative position. Every detail of structure which is common to
the mammalia as a class is found also in man, while he only differs from
them in such ways and degrees as the various species or groups of
mammals differ from each other. If, then, we have good reason to believe
that every existing group of mammalia has descended from some common
ancestral form--as we saw to be so completely demonstrated in the case
of the horse tribe,--and that each family, each order, and even the
whole class must similarly have descended from some much more ancient
and more generalised type, it would be in the highest degree
improbable--so improbable as to be almost inconceivable--that man,
agreeing with them so closely in every detail of his structure, should
have had some quite distinct mode of origin. Let us, then, see what
other evidence bears upon the question, and whether it is sufficient to
convert the probability of his animal origin into a practical certainty.

_Rudiments and Variations as Indicating the Relation of Man to other
Mammals._

All the higher animals present rudiments of organs which, though useless
to them, are useful in some allied group, and are believed to have
descended from a common ancestor in which they were useful. Thus there
are in ruminants rudiments of incisor teeth which, in some species,
never cut through the gums; many lizards have external rudimentary legs;
while many birds, as the Apteryx, have quite rudimentary wings. Now man
possesses similar rudiments, sometimes constantly, sometimes only
occasionally present, which serve intimately to connect his bodily
structure with that of the lower animals. Many animals, for example,
have a special muscle for moving or twitching the skin. In man there are
remnants of this in certain parts of the body, especially in the
forehead, enabling us to raise our eyebrows; but some persons have it in
other parts. A few persons are able to move the whole scalp so as to
throw off any object placed on the head, and this property has been
proved, in one case, to be inherited. In the outer fold of the ear there
is sometimes a projecting point, corresponding in position to the
pointed ear of many animals, and believed to be a rudiment of it. In the
alimentary canal there is a rudiment--the vermiform appendage of the
caecum--which is not only useless, but is sometimes a cause of disease
and death in man; yet in