308 THE CAUSES OF ‘THE xt 
reduce this notion of a horse that we now have, to 
some such kind of simple expressions as can be at 
once, and without difficulty, retained in the mind, 
apart from all minor details. If I make a trans- 
verse 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 
Vigo mass of bones that 
y 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 (¢, Fig. | 
1); and then you 
see, there would be > 
a kind of double — 
ia tube, the whole 
; being inclosed with- ~ 
in 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 (¢); and here I shall 
have the legs proceeding from each side. For ~ 
simplicity’s sake, I represent them merely as — 
