Page:Popular Science Monthly Volume 16.djvu/864

 trained. Again, a dog is the most intelligent animal there is, and he has a large brain in comparison to the size of his body. On the other hand, however, if we examine some of the Monotremata, we find, as already stated, that the brain is very large in proportion to the size of the body; but the animals of this group would by no means be taken as a standard of animal intelligence. It appears very probable, therefore, that in young animals and in the lower classes of the vertebrates the size of the brain has comparatively little to do with the intelligence the animal possesses, but that in the higher vertebrates there is some relation between the amount of intelligence and the quantity of brain matter. The question may be asked. Why is it that the elephant, since it has the largest brain of any land animal, is not the most intelligent animal there is—more intelligent even than man, if the intelligence of an animal depends on the amount of its brain-matter? The answer to this question is easy. This animal being so large requires proportionally larger nerves and larger nerve-centers, to supply the muscles and sensory organs of his body, in the same manner that a larger magneto-electric machine is required when twenty electric lights have to be supplied by it than when it has to supply only ten. The elephant has, in reality, a smaller quantity of brain material available for his intelligence than the dog, because the dog has a much smaller body, and requires smaller nerves. Moreover, the intelligence, it has been proved, is situated in the upper part of the brain, or cerebrum, as it is called. Now, the dog's cerebrum is very much larger, in proportion to the size of his body, than that of the elephant, after allowing for the general law that larger animals have smaller brains in proportion to their body than smaller ones have. The number of smooth and tortuous eminences called convolutions, separated by grooves, which cover the whole surface of the upper brain or cerebrum has also been proved to have something to do with the amount of intellect of the animal. The brains of those animals which possess superior intellect are generally more highly convoluted and more deeply divided by the grooves than those of lower intellect. This may be very well seen by comparing the brains of the horse and the ox. It will at once be seen on looking at the brains of those two animals that the horse's brain is the more convoluted and altogether the more complex structure of the two. The same thing may be seen in the brain of the pig on comparing it with that of the sheep. As an example of brains where the convolutions are few in number and the grooves between them very shallow, we may take those of the echidna and ornithorhynchus, already mentioned as being very large in proportion to their bodies, while they themselves are of a low type. The intellect of those animals evidently does not correspond to the size of their brain. The probability is, therefore, that their brain-matter is of a low type and consequently a larger quantity of it is required. Besides these examples cited there are many more that could be brought forward. It may be stated