THE CEREBRUM, AND ITS FUNCTIONS. 751 



there are many reasons why it is not fair to estimate the relative develop- 

 ment of the Cerebrum by the proportion which it bears to the whole bulk of the 

 animal; and, on the whole, the most accurate basis of comparison would proba- 

 bly 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 Corpora 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 dis- 

 placement of liquid. But the Cerebrum varies in different classes and orders 

 of Vertebrata, not merely in proportional size, but also in the relative develop- 

 ment of its anterior, middle, and posterior lobes. This is a point of very great 

 importance in determining the value to be assigned to the organological system 

 of Gall and Spurzheim and their followers. The Cerebrum of the Oviparous 

 Vertebrata is not a miniature representative of that of Man, as a whole, but only 

 of his anterior lobes; as is sufficiently obvious from an examination of its con- 

 nections with other parts, and from the absence of any other commissural con- 

 nections between its two hemispheres, than those which are afforded by the 

 Sensory Ganglia. It is in the Implacental Mammals that we find the first rudi- 

 ment of the middle lobes of the Cerebrum, and of the proper intercerebral com- 

 missure, the Corpus Callosum; and even in the Rodents this is but very 

 imperfectly developed. As we ascend the Mammalian series, we find the 

 Cerebrum becoming more and more elongated posteriorly by the development 

 of the middle lobes, and the intercerebral commissure becomes more complete; 

 but we must ascend as high as the Carnivora before we find the least vestige of 

 the posterior lobes ; and the rudiment which these possess, and which is enlarged 

 in the Quadrumana, only attains its full development in man, in whom alone 

 the posterior lobes extend so far backwards, as completely to cover in the Cere- 

 bellum. 1 The attention which has yet been given to this department of inquiry 

 has not hitherto done more than confirm the statement already made with regard 

 to the general correspondence between the development of the Cerebrum and 

 the manifestations of Intelligence ; very decided evidence of which is furnished 

 by the great enlargement of the Cerebrum, and the corresponding alteration in 

 the form of the Cranium, which present themselves in those races of Dogs most 

 distinguished for their educability, when compared with those whose condition 

 approximates most closely to what was probably their original state of wildness. 

 783. This general inference, drawn from Comparative Anatomy, is borne out 

 by observation of the Human species. When the Cerebrum is fully developed, 

 it offers innumerable diversities of form and size among various individuals ; and 

 there are as many diversities of character. It may be doubted if two individuals 

 were ever exactly alike in this respect. That a Cerebrum which is greatly un- 

 der the average size is incapable of performing its proper functions, and that 

 the possessor of it must necessarily be more or less idiotic, there can be no rea- 

 sonable doubt. On the other hand, that a large well-developed Cerebrum is 

 found to exist in persons who have made themselves conspicuous in the world in 



1 It lias been asserted by the followers of Gall that the development of the Cerebrum 

 from behind forwards, as above described, is rather apparent than real ; the whole organ 

 being in fact pushed backwards by the excessive development of the anterior lobe. But 

 the anatomical distinction between the anterior and middle lobes is sufficiently obvious 

 externally ; and that of the middle and posterior lobes is also clearly marked out by the 

 development of the posterior cornua of the lateral ventricles, and the situation of the hip- 

 pocampus major. Hence the facts above stated do not admit of any such interpretation ; 

 and they are fully borne out by the history of the Embryonic development of the Cerebrum 

 in Man, which precisely follows the above plan. It is not here denied that the anterior 

 lobe of the Human Cerebrum is remarkable for its great extension forwards ; but still, the 

 difference between the Cerebrum of Man and that of the lower Mammalia consists much 

 rather in the proportional development of the posterior lobes than in that of the anterior. 



