AND THEIR FUNCTIONS. 177 



with the sensory organs, and considered it to be a peculiar 

 organ second in importance only to the heart. 



His views on the spinal marrow were almost entirely 

 erroneous. He considered it to be different from ordinary 

 marrow, but decided that it required to be composed of a 

 glutinous and sinewy substance, to enable it to assist in 

 holding the vertebrae together.* He says that there were 

 some who, seeing that the brain and spinal marrow were 

 continuous, concluded that the brain consisted of marrow, 

 but, he says, they are quite different in character, the 

 marrow being hot and the brain cold, so that the marrow 

 moderates the action of the brain, t 



Aristotle gives some interesting information about the 

 brain and its membranes in certain animals. In Man, 

 and other animals which have a brain, he says, it lies in the 

 front part of the head, the back of the head being empty to 

 an extent varying with the size of the animal, but Man has 

 a brain which, considering his size, is larger and moister 

 than that of any other animal. I 



His views on the nature of the organ of hearing probably 

 induced him to believe in the existence of an air cavity in 

 the back of the head, for he says that the so-called empty 

 space at the back of the head contains air, that the organ of 

 hearing is of air, and that a duct connects each ear with the 

 back of the head. He may also have been influenced by 

 statements, in a treatise by Hippocrates,!! and one probably 

 by a contemporary of Hippocrates, IT that the brain lies 

 more towards the front than the back of the head, which 

 contains only a small amount of brain. 



His estimate of the relative size of the human brain is 

 not quite true. The average weight of the brain of an 

 adult man to his total weight is as 1 to 45 about ; the 

 corresponding ratios for the long-tailed field mouse, house 

 martin, and sparrow are about 1 to 30, 1 to 33, and 1 to 30 

 respectively, and the brain of the goldfinch or the blue tit 

 is relatively still larger. It will be seen that all these are 

 small animals. 



It is not true that the brain of Man is moister than that 

 of other animals, but Aristotle s statement is in accordance 

 with his ideas of the cooling function of the brain. Dr. 



* P. A. ii. c. 6, 6516 and 652a. f Ibid. ii. c. 7, 652a. 

 I H. A.i.c. 7, i. c. 13, s. 2 ; P. A. ii. c. 7, 653a. 

 P. A. ii. c. 10, 6566. |] On Wounds in the Head, c. 2. 



IT On Diseases, ii. c, 8. 



N 



