GENERATION OF ANIMALS, II. vi. 



the brain which extend thither from the heart, the 

 eye, by way of contrast, is the only one of the 

 sense-organs which has a special " body " of its 

 own. It is fluid and cold ; and, unlike the other 

 parts, which are present in their places potentially 

 to begin with and later on come to be formed in 

 actuality, this one is not there at the start,*^ but it 

 is produced by the purest part of the liquid around 

 the brain being secreted off through those passages ^ 

 which are to be observed leading from the eyes to the 

 membrane around the brain. A sure sign of this is 

 that beside the brain there is no part in the head 

 except the eye which is cold and fluid. Hence it 

 is due to necessity that this region gets large at first 

 but shrinks later on ; because the same happens 

 to the brain : at first this is fluid and large, but 

 as evaporation and concoction proceed it becomes 

 more solid and shrinks ; so does the size of the 

 eyes. From the outset the head is very large, on 

 account of the brain, and the eyes, as we see, are 

 large on account of the fluid in them. But the 

 eyes are the last of all to reach their completion, 

 because the brain (on which they depend) does not 

 " set " at all easily ; it is quite late before it ceases 

 to be so cold and fluid ; and this is true of all animals 

 that have a brain, especially of man. That is why 

 the bregma '^ is the last of the bones to be formed : 

 even after the embryos are brought to birth, this 



° Aristotle's knowledge that the eye is an offshoot from the 

 brain, and does not originate in the position which it finally 

 occupies, is indeed remarkable. 



' These are no doubt the optic nerves. 



\ Cf. P.A. 653 a 34 and H.A. 491 a 31. This is the bone 

 which finally grows over the space at the top of the skull 

 known as the " anterior fontanelle." 



227 



