696 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



reasoning, that are quite comparable with those of a child when first learning 

 to talk. ' 



564. This development of the Intelligence under the influence of Man, 

 and in accordance with his habits rather than with the original habits of 

 their species, is yet more remarkable in the case of those Mammals whose 

 instincts lead them to attach themselves peculiarly to him, and whose powers 

 of reasoning are called forth in adapting themselves to the new circumstances 

 in which they are thus placed. The actions of a Dog, a Horse, or an Ele- 

 phant, are evidently the result, in many instances, of a complex train of 

 reasoning, differing in no essential respect from that which Man would per- 

 form in similar circumstances; so that the epithet " half-reasoning," com- 

 monly applied to these animals, does not express the whole truth ; for 

 their mental processes are of the same kind with those of Man, and differ 

 more in the degree of comprehensiveness of their data and conclusiveness of 

 their inferences, than they do in their essential character. We have no evi- 

 dence, however, that any of the lower animals have a voluntary power of 

 directing their mental operations at all similar to that which man possesses; 

 these operations, indeed, seem to be of very much the same character as 

 those which we perform in connected dreams, different trains of thought 

 commencing as they are suggested, and proceeding according to the usual 

 laws until some other disturb them. Although it is customary to regard 

 the Dog and the Elephant as the most intelligent among the lower animals, 

 it is not certain that we do so with justice; for it is very possible that we 

 are misled by that peculiar attachment to Man, which in them must be 

 termed an instinct, and which enters as. a motive into a large proportion of 

 their actions ; and that, if we were more acquainted with the psychical char- 

 acters of the higher Quadrumana, we should find in them a greater degree 

 of mental capability than we now attribute to them. One thing is certain, 

 that the higher the degree of Intelligence which we find characteristic of a 

 particular race, the greater is the degree of variation which we meet with in 

 the characters of individuals; thus everybody knows that there are stupid 

 Dogs and clever Dogs, ill-tempered Dogs and good-tempered Dogs, as 

 there are stupid Men and clever Men, ill-tempered Men and good-tem- 

 pered Men. But no one could distinguish between a stupid Bee and a 

 clever Bee, or between a good-tempered Wasp and an ill-tempered AVasp, 

 simply because all their actions are prompted by an unvarying Instinct. 



565. In estimating the relative development of the Cerebrum in different 

 tribes of Animals, and in comparing this with their relative intelligence, it 

 must be borne in mind that the size of the organ does not, considered alone, 

 afford a means of accurate judgment as to its power. For the quantity of 

 vesicular matter which it contains affords the only fair criterion of the lat- 

 ter; and of this we must judge, not merely by the superficial area, but by 

 the number and depth of the convolutions and by the thickness of the cor- 

 tical layer. Again, there are many reasons why it is not fair to estimate 

 the relative development of the Cerebrum by the proportion which it hears 

 to the whole bulk of the animal ; and, on the whole, the most accurate basis 

 of comparison would probably be afforded by the relation between the bulk 

 of the Cerebrum and the diameter of the Spinal Cord. In making any 

 such comparison, -however, the Thalami Optici, Corpora Striata, and Cor- 

 pora Quadrigemina should be excluded from the estimate for reasons now 

 sufficiently apparent; and the bulk of the Cerebrum proper should be alone 

 determined, either by weight or by the displacement of liquid. But the 

 ( Vrebrum varies in different classes and orders of Vertebrata, not merely in 

 proportional si/.e, hut also in the relative development of its anterior, mid- 

 dle, and posterior lobes. This is a point of very great importance, in deter- 



