Hence it appears that the weight of the hemispheres is four times that of the rest of the cerebro-spinal mass, nine times that of the cerebellum, thirteen times that of the cephalic stem of the spinal cord, and twenty-four times that of the spinal cord.
The average weight of the whole brain in man, at adult age, compared to that of his body, is about 1 to 36.[1] This is a larger proportion than that which it holds in most other animals. The average of mammalia is stated by M. Leuret at 1 to 186, of birds 1 to 212, of reptiles 1 to 1,321, and of fishes 1 to 5,668.[2] Thus it appears that the cephalic prolongation of the spinal cord in man is more than twice as heavy, in proportion to the weight of his body, as the whole brain of reptiles, and ten times as heavy as in fishes. There are some exceptions to these general rules, however. Thus, the brain of the field-mouse is to that of its body as 1 to 31, and that of the goldfinch as 1 to 24, while in the canary bird it is as 1 to 14, and in the blue-headed tit as 1 to 12. In these cases, however, the hemispheres form a much smaller proportion of the whole brain than they do in man. In the dolphin the proportions run from one twenty-fifth to one sixteenth. In the elephant the proportion is 1 to 500, which is very high, considering the animal's enormous weight. In the horse the proportion is about the same as in the elephant; in the ass, it is about 1 to 150. From such facts we may infer that there is no connection between the proportional weight of the brain and the degree of intelligence.
The two following tables are taken from a valuable work by M. Serres, of Paris, on the "Comparative Anatomy of the Brain." The first gives the diameter of the spinal cord at the second cervical vertebra. The two following columns give the transverse and antero-posterior diameters of the cerebellum, the dimensions being stated in hundred-thousandths of a French metre, which is about 39 inches of our measure. The fourth column gives, in round numbers, the proportions of the two diameters of the cerebellum to that of the spinal cord, which is reckoned unity, or 1. The second table exhibits the three diameters of the cerebrum, and the diameter of the spinal cord, and the last three columns exhibit the proportions to the spinal cord, as before.
