1885.] 
On the Human Tail. 
4 T 9 
comparing these 320 figures it is easy to count, without any 
chance of error, — 1, the rachidian ganglia ; 2, the myo- 
meres ; 3, the nascent cartilages of the bodies of the 
vertebrae. These three enumerations check and confirm 
each other, since they all three give the same result : the 
human embryo of eight to nine millimetres has thirty-eight ver- 
tebra. 
This result is further confirmed by an examination of the 
photographs of the recent parts, since we readily distinguish 
35 myomeres, and besides a region occupying the external 
fourth part of the tail where the demarcations are no longer 
visible through the skin. But the sections show us that in 
this last quarter, contrary to the opinion of Ecker and His, 
the mesoderm is most distinctly divided into a double range 
of somites extending to the very tip of the tail, presenting 
dimensions regularly decreasing to the 38th somite, which 
measures merely 37 micromillimetres in diameter. 
This faCt is not teratological ; it is fully confirmed by 
various other embryos which I possess, all perfectly normal, 
but slightly differing in age. 
With the exception of the last two all the caudal vertebrae 
have a blasteme of cartilaginous substance, similar, except 
in size, to that of every other vertebra of the series. The 
last two are only indicated by myomeres, perfectly distinct 
from the rest. The extremity of the tail is formed by the 
termination of the medullary tube, covered merely by the 
skin. The dorsal cord extends, therefore, quite close to this 
extremity. 
The last caudal vertebrae have but a very ephemeral 
existence. Already in embryos of 12 millimetres, — that is 
to say, of six weeks, — the 38th, 37th, and 36th vertebrae are 
blended together into a single mass, and the 35th itself has 
no longer very distinct limits. An embryo of 19 millimetres 
has merely 34 vertebrae, the 34th resulting from the fusion 
of the four last. At this moment the tail altogether is 
already much less prominent. 
It results from these faCts that the human embryo during 
the fifth and sixth week of its development is furnished 
with an incontestable tail, regularly conical, elongated, and 
deserving the name in all respeCts. It is deprived of all 
physiological utility, and must rank among the rudimentary 
organs. 
