Page:Popular Science Monthly Volume 40.djvu/367

Rh forward that the point of the nearly straight-running coccyx is pushed against the skin and lifts it up. Inversion has at this time not yet taken place.

From the third to the fourth month the human fœtus receives its clothing of wool-hairs, which penetrate obliquely through the skin, and form hair-lines converging against the tips of the coccygeal lump, and represent there a vertebra. This vertebra—vertex coccygeus—constitutes in several cases observed and described by Ecker and other investigators (Fig. 5) an evident pencil of longer hairs, a real hair-taillet, such as Grecian art gave at the same point to fauns and satyrs. It has already been shown by Eschricht that the converging hair-tuft in the region of the coccyx is analogous to the similar arrangement of hairs on the tails of the mammalia. Chr. A. Voight has expressly noticed the same relation in his treatise on the direction of hairs on the human body (Denkschrift of the Vienna Academy, 1856). "The parts of the skin on which converging tufts are formed," he says, "are either places which were quite bare in the earlier periods of development, or they are spots that covered the prominent bones (or cartilages), the strongly growing parts, like the coccyx, the elbows, and the tip of the ear in animals, or every place toward which an extension of the skin was taking place or had taken place at the time of the development of the hair." This author remarks especially of the coccyx-tuft that, as the hairs become longer, they rise over the surface and form spiral-shaped hair-tufts, like the brushes on the tips of the tails of animals. There is thus again shown a plain original connection between the formation of the tail-shaped attachment and the coccygeal hair-tuft.

There is usually found in the human foetus, above the coccygeal vertebra, a hairless spot, the glabella coccygea, under which often appears later, and is even perceptible in persons of middle age. a depression of greater or less depth, the foveola coccygea, over the origin and significance of which many and often curious hypotheses have been set forth. It was described by Lawson Tait, in a paper read before the Anatomical and Physiological Section of the British Association in 1878. He had found from the examination of several hundred persons that only fifty-five per cent of them were without traces of the depression or "sacral dimple," while it was faintly marked in twenty-two per cent, and well marked in twenty-three per cent. But it seemed to become imperceptible