STRUCTURE OF THE LOBES OF THE CEREBRUM. 383 



with the precisely similar layer of the cortex of the cerebellum 

 as nervous tissue, and as being essentially a felt-like substance 

 composed of the most indirect and finest nerve processes. 



But inasmuch as we must here presuppose a certain quan- 

 titative relation between the product and the producers, i.e., 

 between the grey substance and the nerve corpuscles, which 

 give off the processes, it would appear that this explanation is 

 opposed by the fact, derived from comparative anatomy, that 

 the breadth of the four internal layers of the cortex, which are 

 rich in cells, exhibit in Mammals very variable relations to the 

 breadth of the most external, which consists essentially of the 

 matrix tissue (fig. 234).* Thus in Man this first layer forms 

 only one-tenth to one-eighth ; in Capuchin Monkeys, one-sixth 

 to one-seventh ; in the Dog, one-sixth ; in the Cat, one-fifth ; 

 in the Bat, one-fourth ; in the Calf and Roe-Deer, one-third, of 

 the entire thickness of the cortex of the cerebrum. Moreover 

 its absolute thickness, amounting in Man to 0*25 of a milli- 

 meter, increases in the Bat to 0'30 of a millimeter, to 0'40 of a 

 millimeter in the Calf, and to 0*50 of a millimeter in the Roe- 

 Deer. These facts agree much better with the view that the 

 nerve elements of the cortex are mingled with a non-nervous 

 matrix, the quantity of which, in the more highly organized 

 brains, is materially reduced by the great development of the 

 true active elements. 



The nature of this matrix, which, as in the spinal cord, pre- 

 sents certain points of difference from the non-nervous portion 

 of the white substance, determines the special characters of the 

 grey matter. The nerve cells alone are not sufficient to give it 

 this character ; and moreover they are very numerous in some 

 parts of the medulla (medulla of the island of Reil and of the 

 external capsule), without indicating their presence by the 

 greyness of the matter. The particular shade of grey in the 

 cortex of the cerebrum, however, (putting aside the abundance 



* The preparations referred to were all partially hardened in spirit, 

 then subjected to the action of a 2 per cent, solution of bichromate of 

 potash, then tinted with carmine, washed in alcohol, rendered transparent* 

 by means of oil of turpentine, and finally mounted in Canada balsam 

 (Clarke's method). 



