OF ORGANIC NATURE. 



9 



and then in the same great cavity, there are lodged the 

 heart and all the great A'essels going from it ; and, be- 

 sides 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 ex- 

 pression 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 ali- 

 mentary 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 {b, 

 Fig. 1) there would be the alimentary canal and the 

 heart ; 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 sim- 



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Fl6. 1. 



