TEGUMENTAL ORGANS 



27 



must refer the reader, as I can here only call attention to a few 

 cases. 



Fio. 17. Two YOUNG 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.M., umbilical cord. 



Gerlach records a very remarkable case of tail formation 

 in an otherwise normal human embryo, in the fourth month 

 of intra-uterine life, an age at which, as a rule, the tail-Uke 

 appendage has disappeared. The length of the trunk was 7'6 

 cm., 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 caudse of the lower animals, i.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, e.g. in those of de 

 Maillet, a hereditary tendency was evident. 



