Page:Popular Science Monthly Volume 40.djvu/366

352 and a shrinking of the tail-root. The former process, the wasting of the hindermost section, takes place, according to the later researches of M. Braun in Dorpat, not only in the human embryo, but also in other vertebrates. "I find," says this naturalist, in his Researches in the Development-History of Parrots (Transactions of the Physico-Medical Society of Würzburg, new series, vol. xv), "in the embryos of swine, cats, sheep, rabbits, mice, and dogs, a long thread at the hinder end of the tail which is sharply distinguished by its tenuity from the rest of the member. The spinal or parted chorda end lies in it in the earlier stage; later it consists only of epidermis cells; and finally it disappears altogether. By this, proof is given that in mammalia as well as in birds the chorda, if I may use the expression, has been carried out too long, and no more vertebræ are formed around its hinder end. It is a striking fact that the long-tailed mammalia are also in this category,"

According to Ecker, who confirms the other features of these observations, this attenuated prolongation, designated as a tail-thread, no longer appears in man; the tail is reduced, much more, according to him, than appears in the sketch, into a conical form. The further wasting process has proceeded so far by the seventh week of the human embryonal life that a tail can no longer be fitly spoken of. Instead of it there is to be seen on the hinder end of the body only a roundish process, the coccygeal lump (Figs. o and 4), on which a few minute excrescences, perhaps rudiments of the atrophied invertebrate part of the tail, are visible. This coccygeal lump retains to the end of the third month the form of an acute isosceles triangle, the broad base of which rises in the region of the coccyx without a clear dividing line, while its point ends over the rectum. Two converging shallow furrows define the lateral boundaries between the coccygeal lump and the buttock, over the level of which it plainly rises. Beyond the rectum begins in the continuation of the median line of this triangle the suture, which in the male embryo extends as a plainly marked selvage over the perinæum. What is called the coccygeal lump in the human fœtus is a prominence so brought