FUNCTIONS OF THE CEREBRUM. 359 



of the vesicular and fibrous substances are in the least altered by this change 

 in their relative position ; indeed the results of observation upon the pheno- 

 mena of disordered Cerebral action are such, as to afford decided confirmation 

 to the idea already propounded, that the action of the vesicular matter con- 

 stitutes the source of nervous power ; whilst the fibrous structure has for its 

 office, to conduct the influence generated in the preceding, towards the points 

 at which it is to operate. The purpose of this arrangement is further evi- 

 denced by the fact, that, in all the higher forms of Cerebral structure, we find 

 a provision for a still greater extension of the surface, at which the vesicular 

 matter and the blood-vessels 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 distinguished. These are, -first, the radiating fibres, which connect the 

 vesicular matter of the cortical substance of the hemispheres with the Thala- 

 mi Optici, and which, if our view of the function of the latter be correct, 

 maybe regarded as ascending or sensory; second, the radiating fibres, 

 which connect the vesicular matter of the cortical substance of the hemi- 

 spheres with the Corpora Striata, and which, on similar grounds, may be re- 

 garded 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 substance 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 functions 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.* 



473. With regard to the Radiating fibres, which connect the Corpora 

 Striata and Thalami Optici with the vesicular surface of the Cerebral hemi- 

 spheres, it must be admitted that 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 how- 

 ever probable such a continuity may be regarded on some grounds, there are 

 certain phenomena, which may perhaps be better explained on the idea, that 

 these radiating fibres are of a Commissural nature only, serving to connect the 

 vesicular matter of the Cerebrum with that of the different portions of the Cranio- 

 Spinal Axis (under which term are included the Spinal Cord, the Medulla 



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 intel- 

 lectual 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 mat- 

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



