22 THE DESCENT OF MAN. 



"a sort of dolmen at Argenteuil, observed twenty-five per cent, to 

 "be perforated; and M. Pruner-Bey found twenty-six per cent, in 

 "the same condition in bones from Vaureal. Nor should it be left 

 "unnoticed that M. Pruner-Bey states that this condition is com- 

 'mon in Guanche 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 ani- 

 mal-like progenitors. 



In man, the os coccyx, together with certain other vertebrae here- 

 after to be described, though functionless as a tail, plainly repre- 

 sent 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 (Pig. 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 including only four vertebrte, 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 fur- 

 nished with some small muscles; one of which, as I am informed 

 by Prof. Turner, has been expressly described by Theile as a ru- 

 dimentary 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 downwards as the 

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

 (the filum terminals) 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 un- 

 doubtedly homologous with the spinal cord; but the lower part ap- 

 parently consists merely of the pia mater, or vascular investing 

 membrane. Even in this case the os coccyx may be said to possess 

 a vestige of so important a structure as the spinal cord, though no 

 longer enclosed within a bony canal. The following fact, for which 

 I am also indebted to Prof. Turner, shows how closely the os coc- 

 cyx corresponds with the true tail in the lower animals: Luschka 

 has recently discovered at the extremity of the coccygeal bones a 

 very peculiar convoluted body, which is continuous vrfth the mid- 

 dle sacral artery; and this discovery led Krause and Meyer to ex- 

 amine the tail of a monkey (Macacus), and of a cat, in both of 



== Quatrefages has lately collected the evidence on this subject. 

 'Revue des Cours Scientifiques,' 1867-1868, p. 625. In 1840 Fleisohmann 

 exhibited a liuman foetus bearing- a free tail, which, as is not always 

 the case, Included vertebral bodies; and this tail was critically exam- 

 ined by the many anatomists present at the" meeting of naturalists at 

 Erlangen (see Marshall in Nledeiiandischen Archiv fur Zoologie, De« 

 cember, 1871.) 



^ Owen, 'On the Nature of Limbs,' 1849, p. 114. 



