742 OP THE FUNCTIONS OF THE NERVOUS SYSTEM. 



probably to allow the vesicular matter to be disposed in such a manner as to 

 present a very large surface, instead of being aggregated together in a more 

 compact mass ; and by this means to admit, on the one side, the more ready 

 access of the bloodvessels which are so essential to the functional operations of 

 this tissue, as well as the more ready communication, on the other, with the vast 

 number of fibres by which its influence is to be propagated. There is no reason 

 whatever to believe that the relative functions of the vesicular and fibrous sub- 

 stances are in the least altered by this change in their relative position ; indeed 

 the results of observation upon the phenomena of disordered Cerebral action are 

 such as to afford decided confirmation to the doctrine already propounded, that 

 the action of the vesicular matter constitutes the source of nervous power, whilst 

 the fibrous structure has for its office to conduct the influence generated in it 

 towards the points at which this is to operate. The purpose of this arrangement 

 is further evidenced by the fact that, in all the higher forms of Cerebral struc- 

 ture, we find a provision for a still greater extension of the surface at which the 

 vesicular matter and the bloodvessels may come into relation ; this being effected 

 by the plication of the layer of vesicular matter into " convolutions/' into the 

 sulci between which the highly vascular membrane known as the " pia mater" 

 dips down, sending multitudes of small vessels from its inner surface into the 

 substance it invests. In the fibrous or medullary substance of which the great 

 mass of the Cerebrum is composed, three principal sets of fibres may be distin- 

 guished. These are first, the radiating fibres, which connect the vesicular 

 matter of the cortical substance of the Hemispheres with the Thalami Optici, 

 and which, if our view of the function of the latter be correct, may be regarded 

 as ascending or sensory ; second, the radiating fibres, which connect the vesi- 

 cular matter of the cortical substance of the Hemispheres with the Corpora 

 Striata, and which, on similar grounds, may be regarded as descending or motor ; 

 and third, the Commissural fibres, which establish the connection between 

 the opposite Hemispheres, and between the different parts of the vesicular sub- 

 stance of the same side, especially between that disposed on the surface of each 

 hemisphere, and those isolated patches which are found in its interior. It is 

 on the very large proportion which the Commissural fibres bear to the rest, that 

 the bulk of the Cerebrum of Man and of the higher animals seems chiefly to 

 depend ; and it is easy to conceive that this condition has an important relation 

 with the operations of the Mind, whatever be our view of the relative func- 

 tions of different parts of the Cerebrum. It appears, from the late researches 

 of M. Baillarger, that the surface and the bulk of the cerebral hemispheres 

 are so far from bearing any constant proportion to each other, in different 

 animals, that, notwithstanding the depth of the convolutions in the Human 

 Cerebrum, its bulk is 2 times as great in proportion to its surface, as it is in 

 the Rabbit, the surface of whose Cerebrum is smooth. The entire surface of 

 the Human Cerebrum, when the convolutions are unfolded, is estimated by 

 him at about 670 square inches. 1 - 



775. With regard to the Radiating fibres, which connect the Corpora Striata 

 and Thalami Optici with the vesicular surface of the Cerebral hemispheres, no 

 positive proof has yet been obtained of their direct continuity with those which 

 enter into the composition of the nerves proceeding from the Spinal Cord and 

 Medulla Oblongata; and we have seen ( 753) that there ae certain phenomena, 



1 The inference drawn by M. Baillarger from the facts he has collected namely, that 

 the proportional surface of vesicular matter in different animals, whether considered abso- 

 lutely, or relatively to the volume of the Cerebrum, has no correspondence with their 

 intellectual capability is far too sweeping an assumption ; since, as above shown, the 

 increase in the Commissural fibres, causing an augmentation of the bulk of the Cerebrum, 

 may be alike the cause of increased intelligence and of a diminished proportional amount 

 of vesicular matter ; though the latter still remains as the original source of power. 



