tive width,—as shown by measurements taken in its natural state and position, not when it is disturbed and displaced,—a statement somewhat differing from that usually made. In the Chimpanzee, proportionally less of the under surface of the cerebrum is seen on each side of the cerebellum, than in man; but posteriorly, though the area of cerebral surface seen, is less in this animal than in man, yet the antero-posterior measurement of the surface is, in proportion to that of the entire brain, greater in the Chimpanzee, being about 19th of the total length of the cerebrum, and, we may add, 17th the distance from the point of the middle lobe to the posterior end of the cerebrum, instead of 111th and 18th respectively, as in man. As to the medulla oblongata, it is less fore-shortened in this basal view of the Chimpanzee's brain, than in man's, because it inclines a little more backwards. In harmony with Sœmmerring's law, the width of the medulla at its base is, proportionately to that of the cerebrum, wider in the Chimpanzee's, than in the human, brain.
If, finally, we take as a sort of arbitrary central point for the entire cerebral mass, the centre of its common stalk, the medulla oblongata, where it intersects the pons; and imagine lines drawn thence to the extreme occipital, frontal, parietal and vertical points of the cerebrum, we find that, in the Chimpanzee, the actual lengths of those cerebral radii, as they might be called, are respectively, 23, 29, 26, and 29 tenths of an inch, whereas, in man, they are 33, 43, 39 and 46 tenths of an inch. These numbers show, not only, the absolutely, far greater size of the human cerebrum, but taking its size as the standard, they show that the deficiency of the Chimpanzee's cerebrum, is most marked in the vertical radius, next in the parietal, then in the frontal, and least of all, in the occipital. In other words, the superiority of development of the human cerebrum follows the same order, as to regions,—being greatest in the vertical and parietal combined, next in the frontal, and least of all, in the purely occipital regions. The numerical ratios of these and other measurements will be found in the following Tables. In Table I. the ratios are given in reference to the human measurements as units; a plan which I cannot but think is preferable to that of making every separate animal's brain a separate unit of comparison with man's.
Table I.
Measurements of the parts of the Encephalon in Man and the Chimpanzee, given in 110ths of an English inch, with the ratios between them, taking the human measurements as units.
Cerebrum.
|
in Man 50, in Chimpanzee 37 = 1 to ⋅74 | ||
|
„65,„44 = 1 to ⋅68 | ||
|
„45,„29 = 1 to ⋅65 | ||
|
„23,„15 = 1 to ⋅65 | ||
|
„35,„20 1 to ⋅57 | ||
