Chap. IV. MANNEK OF DEVELOPMENT. 125 



qnently in ancient than in recent crania, especially as 

 Canestrini has observed in those exhumed from the 

 Drift and belonging to the brachycephalic type. Here 

 again he comes to the same conclusion as in the ana- 

 logons case of the malar bones. In this and other 

 instances presently to be given, the cause of ancient 

 races approaching the lower animals in certain cha- 

 racters more frequently than do the modern races, 

 appears to be that the latter stand at a somewhat greater 

 distance in the long line of descent from their early 

 semi-human progenitors. 



Various other anomalies in man, more or less analo- 

 gous with the foregoing, have been advanced by dif- 

 ferent authors 37 as cases of reversion; but these seem 

 not a little doubtful, for we have to descend extremely 

 low in the mammalian series before we find such struc- 

 tures normally present. 38 



37 A whole series of cases is given by Isid. Geoffroy St.-Hilaire, 

 ' Hist, des Anomalies,' torn. iii. p. 437. 



38 In my ' Variation of Animals under Domestication' (vol. ii. p. 57) 

 I attributed the not very rare cases of supernumerary mammae in 

 women to reversion. I was led to this as a probable conclusion, by the 

 additional mammae being generally placed symmetrically on the breast, 

 and more especially from one case, in which a single efficient mamma 

 occurred in the inguinal region of a woman, the daughter of ano.ther 

 woman with supernumerary mammas. But Prof. Preyer (' Der Kampf 

 nm das Dasein.' 1869, s. 45 ) states that mammas erratics have been 

 known to occur in other situations, even on the back ; so that the force 

 of my argument is greatly weakened or perhaps quite destroyed. 



With much hesitation I, in the same work (vol. ii. p. 12), attributed 

 the frequent cases of polydactylism in men to reversion. I was partly 

 led to this through Prof. Owen's statement, that some of the Ichthy- 

 opterygia possess more than five digits, and therefore, as I supposed, had 

 retained a primordial condition ; but after reading Prof. Gegenbaur's 

 paper (' Jenaischen Zeitschrift,' B. v. Heft 3, s. 341 ), who is the highest 

 authority in Europe on such a point, and who disputes Owen's con- 

 clusion, I see that it is extremely doubtful whether supernumerary 

 digits can thus be accounted for. It was the fact that such digits not 

 only frequently occur and are strongly inherited, but have the power 

 of regrowth after amputation, like the normal digits of the lower verte- 



