460 THE ASCENT OF MAN. 



Every animal possessing a b;ickbone niny be said to be formed by the 

 union of a series of disk like segments arranged on a longitudinal axis. 

 These segments are originally similar in character, bnt become specially 

 modified in innumerable ways to meet the needs of the individual. 

 Anatomists conclude, upon surveying the whole field, that this indicates 

 a derivation of the vertebrates from some form of the annelid worms, 

 among which a single unit produces by successive budding a compound 

 longitudinal body. This view is fully confirmed by the behavior of the 

 human embryo. 



The number of the segments varies considerably, rising sometimes to 

 as many as three hundred in some fishes and reptiles, and being gen- 

 erally greater in the animals below man. There are many indications, 

 however, that in man, segments formerly possessed have disajjpeared. 

 Leaving the skull for the present out of account, there are in the adult 

 thirty-three or thirty-four vertebra3 that may be held to represent these 

 segments; the additional vertebra, when it occurs, almost invariably 

 belonging to the coccygeal or caudal series. In the human embryo 

 thirty-eight segments can at one time be made out. Fouror five of these 

 generally disappear, but cases are by no means wanting in which they 

 remain until after birth and constitute a well-marked free tail. In one 

 case, carefully examined and described by Lissner, a girl of 12 years had 

 an appendage of this character 12.5 centimetres (very nearly 5 inches) 

 long. Other observers, probably less careful and exact, report much 

 greater lengths. From some observations it would appear that abnor- 

 mities of this kind may be transmitted from parent to offspring. 



Dr. Max Bartels recently collected from widely scattered literature 

 reports of 116 actually observed and described cases of tailed men. In 

 o5 instances, authors reported such abnormities to be possessed by an 

 entire people, they themselves having observed certain individuals. 

 These cases are scattered throughout the whole of the known globe and 

 extend back for a thousand years. When we consider that the authen- 

 ticity of many cases is beyond question, and that the number that 

 escaped accurate observation and report must be much greater, we can 

 see that we are not dealing with a phenomenon that is so rare as has 

 generally been supposed. 



Other regressive structures are abundant in this region. The spinal 

 cord in its earlier state extended the entire length of the vertebral canal. 

 In the child at birth it occupies only 85 per cent, of that length ; in the 

 adult 75 per cent. This is due mainly to the more rapid growth of the 

 spine. There stretches however from the lower end of the cord down 

 to the very end of the spine a small thread-like structure, the Jilum ter- 

 minale, a degenerated vestige of the lower caudal part of the spinal 

 cord. Wiedersheim suggests that the frequent occurrence of degenera- 

 tive disorders in the lower end of the adult cord may be due to a patho- 

 logical extension of the normal atrophy. liauber found in this region 

 traces of two additional pairs of spinal nerves. The vessel that runs 



