FUNCTIONS OF THE BRAIN. oOo 



It Is a remarkable fact, that in vertebrated ani- 

 mals all the organs which are subservient to the 

 sensorial functions are double ; those on one side 

 being exactly similar to those on the other. We 

 see this in the eyes, the ears, the limbs, and all 

 the other instruments of voluntary motion ; and in 

 like manner, the parts of the nervous system which 

 are connected with these functions are all double, 

 and arranged symmetrically on the two sides of 

 the body. The same law of symmetry extends to 

 the brain : every part of that organ, which is found 

 on one side, is repeated on the other ; so that, 

 strictly speaking, we have two brains, as well as 

 two optic nerves and two eyes. But in order that 

 the two sets of fibres may co-operate, and consti- 

 tute a single organ of sensation, corresponding with 

 our consciousness of individuality, it was necessary 

 that a free communication should be established 

 between the parts on both sides : and it is for 

 this purpose, apparently, that a set of medullary 



pulpy matter ; and the smaller, which he terms articulated fibres, 

 having, at regular intervals, dilated portions, connected by narrower 

 filaments, so as to bear a resemblance to strings of pearls. These 

 two kinds of fibres are united by cellular tissue, and a fine network 

 of blood vessels. The nerves of the special senses, that is, the 

 olfactory, optic, and auditory nerves, are composed entirely of arti- 

 culated fibres, which also form the great bulk of the white substance 

 of the brain. But the ordinary nerves contain only the straight 

 cylindrical tubular fibres, which, however, are continuous with the 

 former at their junction with the brain. The grey neurine also con- 

 tains minute articulated fibres, but in less number, of smaller dia- 

 meter, and more irregularly disposed : they are contained in a denser 

 network of blood vessels, and are intermixed with layers of granules, 

 and thin plates of grey pulp. The chemical analysis of neurine 

 shows that it contains a large proportion, (about four fifths of its 

 weight) of water. 



