TEGUMENTAL ORGANS 27 
must refer the reader, as I can here only call attention to a few 
cases. 
Fie. 17.—Two Youna Human EmBryos. 
A, ventral; B, lateral view. (After Ecker.) Both figures are intended to show the 
freely projecting tail (cd.). cp., head; vs., eye; ap’., fore-limb; ap”., hind-limb; 
c.u., umbilical cord. 
Gerlach records a very remarkable case of tail formation 
in an otherwise normal human embryo, in the fourth month 
of intra-uterine hfe, an age at which, as a rule, the tail-like 
appendage has disappeared. The length of the trunk was 7°6 
em., the total length 10°8 cm.; and as the tail (Fig. 18), which 
projected freely from the buttocks, measured from root to tip 17 
mm., it was almost a sixth of the total length of the whole 
embryo. At its thickest part, where it left the body, it was 2 
mm. broad, and it thence gradually narrowed towards its middle. 
Closer examination revealed the following facts:—The caudal 
appendage was not only connected with the last (fourth, and still 
cartilaginous) coccygeal vertebra, but the chorda dorsalis could 
be distinctly traced within it. Muscle bundles were also found, 
which from their whole position could be compared with nothing 
else than the M. curvator caude of the lower animals, 7.e. with 
a true tail muscle. The existence of muscles further justifies 
more recent observations, again, have been made on living subjects, where 
- naturally no precise anatomical data could be obtained. One point can be main- 
tained with certainty, viz. that in some of the observed cases, ¢.g. in those of de 
Maillet, a hereditary tendency was evident. 
