On the Hitman Tail. 
418 
[July, 
If we apply the name of tail to the portion of the vertebral 
column which is situate outside the trunk of the body, it 
must be admitted that from the age of three weeks to that 
of two months and upwards the human embryo is endowed 
with this organ, for at this epoch the coccygial vertebras 
occupy the axis of a cylindro-conical appendage, which is 
very apparent, and which issues from the posterior extremity 
of the trunk. If with His we take the position of the 
anus for a guide the tail will be less long, but is still very 
conspicuous, especially at the age of five to six weeks. 
But it is generally admitted as absolutely demonstrated 
that this caudal appendage of the human embryo never con- 
tains any other vertebrae than those found in the coccyx of 
the adult. Ecker, who gives, in full conviction, the name of 
tail to the posterior extremity of the human embryo, has 
declared that he has never met with any supernumerary 
vertebrae. This author has even studied the well-developed 
tail of a human embryo 9 millimetres in length, . and he 
describes and figures all the terminal part as consisting of 
an amorphous blasteme. His, however, detects here a pro- 
longation of the dorsal cord and of the spinal marrow, but 
no segmentation. Both these authorities admit that beyond 
the 33rd or 34th vertebrae there is no further portion of the 
skeleton. 
On this point the researches of M. Fol have led him to a 
result diametrically opposite to that of his predecessors. 
The error of His is due to the circumstance that the oldest 
embryos which he has examined, those of 7 millimetres have 
exactly 34 myomeres, that is to say 33 vertebrae ; and he 
admits, without any further proof, that this was their 
ultimate condition. 
M. Fol presented to the Academy a summary of his 
anatomical study of a human embryo of 5'6 millimetres, i.e., 
of 25 days old. This embryo had as yet only 33 somites, 
representing 32 vertebrae. There is, therefore, an increase 
in number in the fourth week. This faCt led M. Fol to ex- 
amine if the number did not go on increasing during the 
fifth week, and his expectation was not disappointed. The 
human embryo of from 9 to 10 millimetres, the age when the 
tail attains its greatest prominence, possesses a greater 
number of vertebrce than the adult. 
Two embryos of the finest appearance, and perfectly fresh 
when sent to the author, were first photograped and then 
cut into sections. The series of slices are irreproachable, 
and one of the two, comprising 320 sections, has been most 
carefully drawn in the camera lucida, in its totality. On 
