PARTS OF ANIMALS, II. x. 



they operate. Sight is always located there. The 

 case of hearing and smell in fishes and the like 

 shows that the opinion I maintain is patently correct. 

 These creatures hear and smell, although they have 

 no obvious and visible organs for these senses in the 

 head. As for sight, it is reasonable enough that 

 when present it should always be located near the 

 brain, for the brain is fluid and cold, and the sense- 

 organ of sight is identical in its nature with water, 

 which of all transparent substances is the easiest to 

 keep confined. Again, those senses which are in- 

 tended for more precise work than the others must 

 necessarily receive greater precision by being situ- 

 ated in parts where the blood is specially pure, since 

 the movement of the heat in the blood ousts the 

 activity appropriate to sensation. These are the 

 reasons why the organs of these senses are placed in 

 the head. 



Now the back of the head is free from fleshiness as 

 well as the front. This is because the head is the 

 part which all animals that possess one have to hold 

 as upright as possible. Nothing that carries a burden 

 can raise itself upright, and the head would be 

 burdened if it were well covered ^\dth flesh. And 

 this is another reason to show that the lack of flesh 

 on the head is not for the purpose of enabling the 

 brain to function in sensation. There is no brain in 

 the back of the head, although the back has no more 

 flesh on it than the front. 



Some animals have their organ of hearing as well 

 as of sight located in the region of the head. This is 

 well explained on our view, which is that the organ 

 of hearing is of air. The space in the head called the 

 vacuum is full of air. 



177 



