NERVOUS SYSTEM. 315 



brain, we perceive that its interior presents two substances of 

 different colours: the outer of these, of a dirty greyish hue, is 

 called the cineritious or cortical part ; the inner, which is white, 

 and of which the chief bulk of the organ is composed, the me- 

 dullary. The cortical part (which is, proportionately to the 

 medullary, more prevalent in the brain of the horse than in that 

 of the human subject) is not always the outer — in some places, 

 the relative disposition of the medullary and it being reversed — 

 it is that, however, in which the bloodvessels of the organ are 

 most conspicuous : for, in consequence of being closely invested 

 by the vascular pia mater, it receives the numerous ramifications 

 of arteries transmitted by that membrane for the nourishment of 

 the interior parts of the brain . On the other hand, in the medul- 

 lary portion, the bloodvessels, which in health only convey the 

 colourless parts of the blood, are so minute that they escape no- 

 tice ; unless, occasionally, here and there, when it has been in- 

 flamed, the bloody specks upon its divided surface denote the 

 division of those that have become of sufficient magnitude to 

 admit the red globules. 



According to the investigations of the most accurate anato- 

 mists, the brains of animals appear to be of a fibrous nature; 

 and in many parts of the human brain (which is larger than that 

 of any other animal) the disposition and course of its fibres have 

 been traced : such inquiries, however, have, unfortunately, not 

 led to any elucidation of the sensorial functions, nor are we 

 aware that they have been attended with any advantageous result 

 in regard to its pathology. After all, the truth is, that the inti- 

 mate structure of this organ is still unknown to us. With regard 

 to the cineritious or cortical part, there is much reason to be- 

 lieve, that it is almost wholly constituted of the ramifications of 

 bloodvessels of extreme exility ; from which others, still more 

 minute, are distributed to the substance of the medulla. 



It is here worthy of remark, that in no instance does Nature 

 so invariably present us with the same structure and arrangement 

 of parts as in this viscus : in almost every other in the body, 

 we can discover some little variation, in this respect, in different 

 subjects ; but in the brain, the same uniform appearances ever 

 present themselves on dissection : so intimately united do struc- 

 ture and function seem to be in this organ. 



Duplicity. — The cerebrum is divided into two halves, called 

 hemispheres, each of which is formed of parts precisely sin)ilar, 

 in every particular, to each other; so that, in fact, every part of 

 the organ may be said to be double, i. e. its two halves arc con- 

 stituted of several small portions, which are not only perfectly 



