ii. 10. 45 



head, it is this head which more than any other part requires 

 to be held up. But, were the head heavily laden with flesh, 

 this would be impossible ; for nothing so burdened can be held 

 upright. This fact is an additional proof that the absence of 

 flesh from the head has no reference to brain sensation. For 

 there is no brain in the hinder part of the head,^^ and yet this 

 is as much without flesh as is the front. 



In some animals hearing as well as vision is lodged in the 

 region of the head. Nor is this without a rational explanation. 

 For what is called the empty space is full of air, and the organ 

 of hearing is, as we say, formed of air. Now there are channels ^^ 

 which lead from the eyes to the blood-vessels that surround 

 the brain ; and similarly there is a channel which leads back 

 again from each ear and connects it with the hinder part of 

 the head. But no part that is without blood is endowed with 

 sensation, as neither is the blood itself, but only certain parts 

 formed of blood.^^ So that none of the bloodless parts of 

 sanguineous animals are endowed with sensation, nor their blood 

 itself ; for no such part is sensitive in any animal. 



The brain in all animals that have one is placed in the front 

 part of the head ; because the direction in which sensation acts 

 is in front ; and because the heart, from which sensation proceeds, 

 is in the front part of the body ; and lastly because the instruments 

 of sensation are the blood-containing parts, and the cavity in the 

 posterior part of the skull is destitute of blood-vessels. 



As to the position of the sense-organs, they have been arranged 

 by nature in the following suitable manner. The organs of 

 hearing are so placed as to divide the circumference of the head 

 into two equal halves ; for they have to hear not only sounds 

 which are directly in a line with themselves, but sounds from all 

 quarters. The organs of vision are placed in front, because sight 

 is exercised only in a straight line, and moving as we do in a 

 forward direction it is necessary that we should see before us, 

 in the direction of our motion. Lastly, the organs of srriell are 

 placed with good reason between the eyes. For as the body 

 consists of two parts, a right half and a left, so also each organ 

 of sense is double. In the case of touch this is not apparent, 

 the reason being that the primary organ of this sense is not the 

 flesh or analogous part, but lies internally .^^ In the case of 

 taste, which is merely a modification of touch ^^ and which 

 656 b. 



