than that of the ox. The camel also may be included in this class, as being about the same size. Although many camels are larger, still the bulk of the body is not very much greater than that of the horse and ox. Its brain is very similar in size to that of the ox, but smaller than the horse's brain. The brain of the sheep is a good deal larger than that of the goat, although their bodies are similar in size. The sheep and the pig are also animals which we might classify if we do not take extreme sizes, but compare animals similar in age or bulk. We find that the pig's brain is larger than the sheep's, and corresponds in size very nearly to that of the dog. In the cat the size of the brain, in proportion to the body, is much larger than that of the domestic rabbit, although the size of the two animals is very much the same.
In these examples given we have not taken into consideration the order to which the animal belongs in the vertebrate series, but only compared similar sized animals, and In all cases we have compared the brains of adult animals. This is a very important point, as it is found that in all animals, including man himself, the size of the brain, in proportion to the size of the body, is much greater in young animals than it is in the adult. In some animals the head is found to grow enormously in size as the animal reaches adult age, but the brain does not increase to the same extent. There is generally some reason to be found for this in those animals where it takes place. For example, in the elephant the head of the young animal is by no means out of proportion to the size of its brain; but if we bisect the head of an adult animal we find that the brain only occupies a small cavity, and the rest of the skull is composed of plates of bone with air-cells between them. In the young elephant we find none of those plates and air-cells between the outer and inner layers of cranium, but simply the two layers of bone close to one another; but we will also find that at this stage the young elephant has no large tusks to carry, and its trunk is light, so that its head is comparatively light. The case is, however, quite different in the adult, when there are two large tusks and a large trunk to carry. In order to support this great weight he requires strong muscles. The great increase in the size of his head, therefore, is to afford a requisite extent of surface for the attachment of the muscles. In order to get this, combined with lightness, the skull is composed of those plates and air-spaces mentioned.
A very interesting question, but one which it is very difficult to answer, is whether the intelligence of the animal corresponds to the size of its brain. It is very difficult to make comparisons in many animals, as one animal shows his intelligence in one way, and another in another way. However, going over some of the animals whose brains we have compared, we may take as an example the horse and the ox. The horse has the larger brain, and he has undoubtedly the greater amount of intelligence. We find that horses can be trained to a great extent, as may be seen daily in a circus, but the ox has never been so
