178 AEISTOTLE S ANHOMCEOMEEIA 



Ogle suggests that the statement is based on an examination 

 of the foetal brain.* It is practically certain that Aristotle 

 did not examine an adult human brain, but he may have 

 examined the brain of some animal in which brain a rapid 

 decomposition had set in. I have been informed of a case 

 in which, the brain pan having been removed for the 

 purpose of taking out the brain from a comparatively fresh 

 body, a large part of the brain flowed away. 



Aristotle states that there are two membranes about the 

 brain, a weaker vascular one about the brain itself and a 

 stronger one next the bone ; that the brain is divided into 

 right and left halves ; that the cerebellum at the extreme 

 end of it differs in appearance and texture from the rest of 

 the brain ; and that, in most animals, there is a small 

 cavity in the middle of the brain, t 



There are three membranes about the brain, the inner 

 most being the pia mater, which is intimately associated 

 with the arachnoid membrane or middle membrane, and the 

 outermost being the dura mater. Aristotle probably saw 

 the strong dura mater, and the other two membranes, these 

 two delicate membranes constituting his inner membrane. 

 The cerebellum is somewhat darker than the rest of the brain, 

 and is striated or ribbed externally, while in form it is quite 

 different, as Aristotle says, from the rest of the brain. The 

 statement about the small cavity in the middle of the brain 

 is true as far as it goes. In vertebrates, there are cavities 

 or ventricles (four in Man) within the brain and in com 

 munication with one another. 



In several passages he makes it clear that he believed 

 that the substance of the brain was quite bloodless. I This 

 belief has been used against him by some of his critics. 



It is clear from several passages, e.g., H. A. iii. c. 3, s. 7, 

 that he knew of the presence of blood and blood-vessels in 

 the membranes about the brain, and he says that the brain 

 itself is bloodless, so that he evidently refers to the brain 

 divested of its membranes. This does not, however, over 

 come the difficulty, for if the brain of a mammal, such as a 

 sheep or rabbit, be examined, after removal of the membranes 

 and careful washing, small blood-vessels can be seen ex 

 tending some distance into it. Some have suggested that 

 Aristotle made his observations only on the brain of an 



* Aristotle on the Parts of Animals, 1882, p. 165. 



f H. A. i. c. 13, ss. 2 and B, iii. c. 11, s. 1. 



J H. A. i. c. 13, s. 3, iii. c. 3, s. 8 ; P. A. ii. c. 7, 652a. 



