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Page:Popular Science Monthly Volume 4.djvu/606

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THE POPULAR SCIENCE MONTHLY.

touching the most prominent parts of the forehead and upper jaw, the intersected angle is called the facial angle" (vol. ii., p. 572, "Anatomy of Vertebrates").

The relation of the face is not to the base of the skull, or the plane from the floor of the nostrils to its articulation to the backbone, but to the axis of the body; for the face, in the lowest class of animals that have a backbone, the fish, is in line with the base of the skull, the axis of the body, and the dorsal surface of the animal; and in man, the highest class, the face is in line with the abdominal surface, and axis of the body. But the base of the skull does not keep in harmony, but varies irregularly. Then, there are numerous other elements than the bones at the base of the skull, that are factors in the aspect of the face, as, the modified development of other bones of the skull, peculiar development of bones of the face, and relation of the bones of the face that are not attached to the skull, but to other facial bones.

To make the subject more clearly comprehensible, it will be necessary to trace more in detail the development of the division of animals to be considered.

The subject of the facial angle has occupied the attention of philosophers from the earliest antiquity. Their theories, though vague, unsatisfactory, and uninteresting in themselves, yet tend conclusively to show that some patent general principle underlies the whole domain of the subject. Confined, as they were, to the narrow limits of the varieties of the human race, they would get only a part of the evidence that is so beautifully illustrated, when we include the whole sub-kingdom of animals to which we belong.

At the beginning of the present century, Cuvier, Von Baer, and others, discovered and established the great laws of evolution. The laws thus elucidated were: 1. That the entire animal kingdom originates from an ancestral egg; eggs, too, though differing in physical appearance, that are quite similar in structure. 2. That every animal, in its evolution, had to pass through the several stages of ovulation, fertilization, germination, and development, before it could maintain an independent existence. 3. That in their development they assumed but few primary structural patterns or types.

After the promulgation of the above doctrines, a series of investigations ensued, which brought naturalists to approximate a general agreement that there are only five general morphological or form-types of animals. Every animal, then, of the entire animal kingdom, must be classed in one or the other of these five sub-kingdoms, and each division thus classed has one fundamental plan of structure. The only way in which the animals of each sub-kingdom can differ is in the manner of executing their physiological functions.

In considering, then, any of the great physiological and philosophical questions that are based upon a uniformity of primitive type-development, we find that many useful lessons may be learned by including