oduction, and so on. Let us now
endeavour to reduce this notion of a horse that we now have, to
some such kind of simple expression as can be at once, and without
difficulty, retained in the mind, apart from all minor details. If
I make a transverse section, that is, if I were to saw a dead horse
across, I should find that, if I left out the details, and supposing I
took my section through the anterior region, and through the fore-limbs,
I should have here this kind of section of the body (Fig. 1). Here would
be the upper part of the animal--that great mass of bones that we spoke
of as the spine (a, Fig. 1). Here I should have the alimentary canal
(b, Fig. 1). Here I should have the heart (c, Fig. 1); and then you see,
there would be a kind of double tube, the whole being inclosed within
the hide; the spinal marrow would be placed in the upper tube (a, Fig.
1), and in the lower tube (d d, Fig. 1), there would be the alimentary
canal (b), and the heart (c); and here I shall have the legs proceeding
from each side. For simplicity's sake, I represent them merely as stumps
(e e, Fig. 1). Now that is a horse--as mathematicians would say--reduced
to its most simple expression. Carry that in your minds, if you please,
as a simplified idea of the structure of the Horse. The considerations
which I have now put before you belong to what we technically call the
'Anatomy' of the Horse. Now, suppose we go to work upon these several
parts,--flesh and hair, and skin and bone, and lay open these
various organs with our scalpels, and examine them by means of our
magnifying-glasses, and see what we can make of them. We shall find that
the flesh is made up of bundles of strong fibres. The brain and nerves,
too, we shall find, are made up of fibres, and these queer-looking
things that are called ganglionic corpuscles. If we take a slice of the
bone and examine it, we shall find that it is very like this diagram
of a section of the bone of an ostrich, though differing, of course,
in some details; and if we take any part whatsoever of the tissue, and
examine it, we shall find it all has a minute structure, visible only
under the microscope. All these parts constitute microscopic anatomy
or 'Histology.' These parts are constantly being changed; every part is
constantly growing, decaying, and being replaced during the life of the
animal. The tissue is constantly replaced by new material; and if you go
back to the young state of the tissue in the