Page:Popular Science Monthly Volume 16.djvu/862

 body of any member of the group, but a much smaller brain in proportion to its body than many of the smaller birds. As a class, however, the birds have large brains in proportion to their body, when compared to the other vertebrates, and so present a contrast to the reptiles, in which, as already stated, the brain is small throughout the whole group. In the next class of vertebrates—the Monotremata—the brain is large in proportion to their body, but it must be taken into account that this group contains very few large animals, being composed almost entirely of small ones. The size of the brain in the echidna, and the ornithorhynchus, both belonging to this group, is especially large in proportion to the small bodies which the animals possess. This is more remarkable when we consider the low position they occupy in the vertebrate series. In this manner we might go on through the whole series of vertebrates, showing how the larger animals have relatively smaller brains, and also the reverse, that the smaller animals have larger brains for their size.

We must now consider, however, the relative size of the brain in animals about the same size, as it is only in that way that we can gain information on the subject. Owing to the difficulties which attend the investigation of this subject, comparatively little is accurately known about it. It may be stated generally that the brain of domestic animals is larger than that of wild animals of a corresponding size of body. As an example of this we may take the case of the dog and the wolf. If the brains of those animals are compared, it will be found (if the animals compared are of the same size) that the brain of the dog is the larger. Again, if we compare the brains of a dog, a badger, and a musk-deer about the same size, we find that the brain of the dog is the largest, those of the other two animals being about the same size. It will be observed that, in classifying the size of an animal, we do not go by the height the animal stands, because many animals whose bodies are about the same size differ in height only on account of their legs being longer. In making comparisons, therefore, we compare animals whose bulk is the same, irrespective of the actual height they may stand from the ground. Among the wild animals of a similar size, we also find considerable difference between the comparative size of the brain and that of the body. As an example of this, we may take the case of the lion and tiger. The brain of the lion is much larger than that of the tiger; however, that might be expected from the lion being a larger animal than the tiger; but the brain is much larger in proportion than the difference of size of the two animals would account for: therefore the brain of the lion is larger, in proportion to the size of his body, than that of the tiger is in proportion to his body.

But we must now compare the size of the brains of domestic animals of the same size. Although the horse stands higher than the ox, yet both those animals may be classed together for the comparisons of their brain. We find that the brain of the horse is very much larger