His, but also in the reduction of all essential structures of fioi] 

 the vertebral portion of the tail, i. e. the vertebrae, muscle 

 segments, spinal ganglia and blood-vessels. It is interesting 

 to note that in this tendency to reduction the resemblance 

 between human and other mammalian tails also holds. The 

 caudal filament, as Braun has shown, is present in other 

 embryos and atrophies as development proceeds. The ten- 

 dency to fusion of the distal vertebrae has been observed in 

 the embryos of various long-tailed animals. And in short- 

 tailed varieties, as Bonnet has shown, this tendency is merely 

 accentuated.^^ 



The view that a great many of the anomalous caudal appen- 

 dages found in man are, as stated in the beginning, due to the 

 persistence of the embryonic tail, is warranted by the facts 

 gathered both from the study of the former as well as of the 

 latter. Many of the differences in form are explained by the 

 hypothesis of Bartels that the embryonic tail may be arrested 

 in any stage of its development. The soft or boneless tails 

 are clearly not due to the multiplication of vertebrge or even 

 to the persistence of all which are developed in the embryo, 

 but, as His first suggested, are to be regarded as persisting 

 caudal filaments. The usual position of these appendages 

 as well as their structure support this conclusion. The fact 

 that they are not always attached exactly over the tip of the 

 coccyx cannot be regarded as conflicting with this view, for, 

 as has long been recognized, the curvature in the vertebral 

 column, especially m the sacral and coccygeal regions, changes 

 markedly during development, and the caudal filament not 

 being firmly united to the tip of the coccyx might easily be 

 shifted slightly in relation to the latter. 



In the action of amniotic adhesions Schaeffer has sug- 

 gested a cause which may undoubtedly bring about the per- 

 sistence of the caudal filament, for it is a fact that in many, 



37 R. Bonnet : Die stummelschwanzigen Hunde im Hinblich auf die 

 Vererbimg erworbener Eigenschaften. Zeigler's Beitriige z. path. Anat. 

 u. allg. Pathol., Bd. iv, 1889. 



38 Anatomic menschlicher Embryonen, i, p. 95. 



39 Archiv f. Anthropol., Bd. xx, 1892, p. 219. 



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