INTRODIJCTOKY. 4^31 



All animals are characterised by sensation and motion. The 

 brain and nervous system are the medium by which the func 

 tions of animal life is manifested : while the heart and its acces- 

 sory organs, nutrition and generation, &c. are the vital and vege- 

 tative functions, and are common to animals and plants. Sen. 

 sation, therefore, exists in the nervous system. As we descend 

 in the scale of being, these agents gradually become less perfect, 

 until they at last disappear. In the lowest state of animal ex- 

 istence, the nervous sjstem is invisible, if it exists at all; and 

 the muscular fibre has given way to a shapeless mass of animal 

 matter. 



OF VERTEBRATED ANIMALS. 



From man, who stands at the head of vertebrate animals, in 

 consequence of his perfect organization, down to the lowest of 

 the fish, the brain is encased in a cranium, and the spinal cord 

 is inclosed in a bony articulated column, called the spine. To 

 the sides of the spine the ribs are attached, and the bones of the 

 upper and lower extremities : these are either articulated, or 

 kept together by ligaments. Over these, again, are placed the 

 muscles, which give action to the bones. The alimentary sys- 

 tem is inclosed within the cavity of the ribs and abdomen. 



All vertebrated animals have a muscular heart, red blood; 

 the mouth is constructed with two horizontal jaws ; and organs 

 are situated in the head by which they enjoy, through the me- 

 dium of the nerves, the various senses, namely, of vision, hear- 

 ing, smell, and taste. There is no instance of their having 

 more than four limbs. 



Comparative anatomy enables us to trace a similarity to all 

 the parts of man, through the whole vertebrated animals. 



The organs of sense, in all animals with a spine, consist in 

 two eyes, two eai-s, two nostrils, the tongue, and all the muscle 

 which cover the skeleton. The nervous system takes its rise in 

 two masses situated in the cavity of the skull ; the substance is 

 called medullary, or marrow ; and anatomists have remarked, 

 that its volume is proportioned to the intellectual energy. The 

 true nature of the medullary substance has not yet been ascer- 

 tained by anatomists. When minutely examined, it appears a 

 soft matter, of a cream-coloured white ; and seems lo consist 

 ^of infinitely small globules. It appears itself to be devoid of 



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