CHAP. XI.] FUNCTIONS OF THE CEREBRAL CONVOLUTIONS. 363 



matter which connects them with the optic thalami and corpora 

 striata, form by far the largest portion of the encephalon ; and 

 this fact alone ought to stamp them with great physiological import- 

 ance. The complexity of the convolutions in the animal scale is in 

 the direct ratio of the advance of intelligence. It must be remarked, 

 however, that the weight of the brain, whether absolute, or in 

 relation to the body, affords no criterion, or at best an imperfect one, 

 of the extent of the convoluted surface. Highly complicated con- 

 volutions may exist along with a brain both absolutely and rela- 

 tively small. Thus Leuret asserts, that the ferret, which has several 

 well-marked convolutions on each hemisphere, has a brain no larger 

 than that of the squirrel, which has no convolutions at all, and which 

 wants even the few fissures which mark their first development in 

 the rabbit, the beaver, the agouti, etc. And the last-named ani- 

 mals have the brain both absolutely and relatively larger than that 

 of the cat, the pole-cat, the roussette, the uiiau, the sloth, and the 

 pangolin, all of which possess convolutions. We hence learn the 

 physiological distinctness of these organs from the more deeply- 

 seated gangliform bodies of the brain to which we have already 

 seen that separate functions may be assigned. 



At the early periods of human life, in infancy and childhood, 

 the convolutions of the brain are very imperfectly developed, and 

 their increase of size goes on simultaneously with the advance of 

 mental power. If the former be arrested, or if some congenital 

 fault prevent the further growth of the convolutions, the mental 

 powers are of the lowest and feeblest kind, but little above those of 

 the brute with imperfect convolutions. In all idiots the brain is not 

 only small, but its convoluted surface is extremely limited. 



We remark, here that the convoluted form must be regarded no 

 otherwise than as a convenient mode of packing, which affords an 

 indication of a greater or less superficial extent of vesicular matter, 

 for in cases where a slow and gradual accumulation of water takes 

 place within the ventricles of the brain, when accompanied with cor- 

 responding enlargement of the cranium, the convolutions become 

 unfolded ; and yet the intellect may remain unimpaired, at least so 

 far as the obvious damage to the quality of the nervous matter in 

 such cases will allow. 



In examining the brains in the animal series, we observe a pro- 

 gressive increase in the complication of the convolutions, and there- 

 fore in the extent of the convoluted surface, as we pass from the 

 inferior to the higher classes, from those endowed with but feeble 

 intelligence to those which enjoy sagacity, docility, and memory. 



