*2 THE DESCENT OF MAN 



cent in tte same condition in bones from Vanr^al. Nor 

 should it be left unnoticed that M. Pruner-Bey states that 

 this condition is common in Gruanclie skeletons. " It is an 

 interesting fact that ancient races, in this and several other 

 cases, more frequently present structures which resemble 

 those of the lower animals than do the modern. One chief 

 cause seems to be that the ancient races stand somewhat 

 nearer in the long line of descent to their remote animal- 

 like progenitors. 



In man, the os coccyx, together with certain other ver- 

 tebra hereafter to be described, though functionless as a 

 tail, plainly represent this part in other vertebrate animals. 

 At an early embryonic period it is free, and projects beyond 

 the lower extremities, as may be seen in the drawing (Fig. 1) 

 of a human embryo. Even after birth it has been known, in 

 certain rare and anomalous cases," to form a small external 

 rudiment of a tail. The os coccyx is short, usually includ- 

 ing only four vertebrae, all anchylosed together: and these 

 are in a rudimentary condition, for they consist, with the 

 exception of the basal one, of the centrum alone." They 

 are furnished with some small muscles, one of which, as I 

 am informed by Prof. Turner, has been expressly described 

 by Theile as a rudimentary repetition of the extensor of 

 the tail, a muscle which is so largely developed in many 

 mammals. 



The spinal cord in man extends only as far downward 

 as the last dorsal or first lumbar vertebra; but a thread-like 

 structure (the filum terminale) runs down the axis of the 

 sacral part of the spinal canal, and even along the back of 

 the coccygeal bones. The upper part of this filament, as 

 Prof. Turner informs me, is undoubtedly homologous with 



^'' Quatrefages has lately collected tlie evidence on this subject. "Eevue 

 des Cours Scientiflques, " ISGt-eS, p.' 625. ' In 1840 Fleischmann exhibited a 

 human foetus bearing a free tail, which, as is not always the case, included 

 vertebral bodies ; and this tail was critically examined by the many anatomists 

 present at the meeting of naturalists at Erlangen (see Marshall in Niederland- 

 ischen Archiv fur Zoologie, December, 1871). 



" Owen "On the Nature of Limbs," 1849, p. 114. 



