552 ^ THE POPULAR SCIENCE MONTHLY. 



point and a shrinking of the tail-root. The former process, the 

 wasting of tlie 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 natu- 

 ralist, in his Researches in the Development-History of Parrots 

 (Transactions of the Physico-Medical Society of Wiirzburg, 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 ej)idermis cells ; and finally it disappears alto- 

 gether. 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 vertebree 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 lumjD (Figs. 

 o and 4), on which a few minute 



Figs. 3 AND 4. -Embryos IN THE Coccygeal- excreSCences, perhaps rudiments 

 LUMP rEBioD. Fig. 3, 4-1 cm. long ; Y'm. ^ ,^ , , . t . , , 



4, 14-8 cm. long. From Ecker. o^ ^li© 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 fur- 

 rows 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 perinaeum. What is called the 

 coccygeal lump in the human foetus is a prominence so brought 



* In mammals Ecker sometimes found the tip of the tail-thread so sharp and horny that 

 the name tail-spine seemed to be more appropriate, and he suggests that possibly the well- 

 known tail-spine of the lion is nothing else than the persistent embryonal tail-thread. 



