The elements composing the nutritive case are the jaws, ribs, and pelvic girdle. These, like the spinal elements, are subject to great modification, owing to the immense range of variation to which their specializations are subjected. The difference in the facial developments
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can well be imagined by calling to mind the various countenances of animals, from the fish to man. The angle of the face is simply and properly, I think, indicated by the relation expressed by two lines: the first, or base line, corresponding to the axis of the body; the other, diverging, or face line, drawn from the anterior margin of the upper jaw, over the centre of the forehead. The relation and angles formed by these two lines, and their intersections thus indicated, express the relation and comparative development at the union of the two primitive tubes, the neural, or skull, and hemal (face), at the anterior extremity or head of a vertebrate animal.
As before stated, authors have hitherto established the base-line from the floor of the nostrils, to the articulation of the occipital bone to the vertebra?. This is a grave error, and one, no doubt, that has contributed its share to depreciate the subject as an index to the mental caste of a vertebrate animal. For, by adopting this method, we are subject to the enormous error of ninety degrees in passing through the sub-kingdom, all of which we lose, little by little, as we ascend the scale of animals of this type, or form of structure. And yet they make this application through the entire vertebrate series. Yet, by referring to the cut, we find the face of the lowest class of the type, the fish, to be in direct line with the dorsal surface of the animal, and hence the base and diverging lines are parallel; while, in the highest of the type, that of man, the face is in line with the ventral or abdominal surface. Again, after effecting a grand variation of one hundred and eighty degrees, or the half of a circle, the two lines are once more parallel.
What, then, are the factors in the phenomena of the great change of the aspect of the face, with such a modification of its constituents, from a line of the dorsal to that of the abdominal surface, all of which is effected by almost imperceptible gradations, as we ascend the series from the fish to man? It is by the modification of the anterior extremities of these cranio-vertebral canals in the development and increase of the cerebral hemispheres, which is that part of the brain that is recognized as the seat of thought, and their influence upon other
