is called the spine, and those in front are the ribs; and then there
are two pairs of limbs, one before and one behind; and there are what
we all know as the fore-legs and the hind-legs. If we pursue our
researches into the interior of this animal, we find within the
framework of the skeleton a great cavity, or rather, I should say, two
great cavities,--one cavity beginning in the skull and running through
the neck-bones, along the spine, and ending in the tail, containing the
brain and the spinal marrow, which are extremely important organs. The
second great cavity, commencing with the mouth, contains the gullet,
the stomach, the long intestine, and all the rest of those internal
apparatus which are essential for digestion; and then in the same great
cavity, there are lodged the heart and all the great vessels going from
it; and, besides that, the organs of respiration-- the lungs: and then
the kidneys, and the organs of reproduction, 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