PARTS OF ANIMALS, II. x. 



Passages (or channels) run from the eyes to the 

 blood-vessels that are round the brain. And, again, 

 a passage runs from the ears and connects to the 

 back of the brain. 



[No bloodless part is capable of sensation, nor 

 indeed is the blood itself. It is the parts which are 

 made out of blood that have this faculty. Hence, 

 in the blooded animals, no bloodless part is capable 

 of sensation, nor indeed is the blood itself, for it is 

 no part of animals.] ^ 



The brain, whenever there is one, is in the forepart 

 of the head. This is (a) because all acts of sensation 

 take place in a forward direction ; (6) because the 

 heart, from which sensation has its origin, is in the 

 forepart of the body ; and (c) because the process 

 of sensation depends upon parts that have blood 

 in them, whereas the sac at the back of the head 

 contains no blood-vessels at all. In fact. Nature 

 has located the sense-organs in a very satisfactory 

 manner. The ears are half-way round the circum- 

 ference of the head, because they are to hear sounds 

 from all directions alike and not only from straight 

 before them. The eyes face front : this is because 

 sight is along one straight line, and we must be able 

 to see along the line in which we are moving, which 

 is directly forward. The nostrils are between the 

 eyes, and this is quite reasonable. Each of the 

 sense-organs is double, because the body itself is 

 double : it has a right side and a left side. It must 

 be admitted that this duality is not at all clear in the 

 case of touch : this is because the primary sense- 

 organ of touch is not the flesh or a corresponding part, 

 but something internal. With the tongue the duality 

 is not very clear, but more so than with touch. 



179' 



