1892.] The Contemporary Evolution of Man, 475 



ent iroly different class of congenital variations whicli may In- 

 described as fortuitous or indefinite because they do not omir 

 in any fixed percentage 1 of cases; they are liable to take any 



are not found in the hypothetical atavus, and there ifl DO* 

 sufficient evidence to cause us to consider them as incipient 

 features of our future structure. 



Some may not be truly congenital (i.e., springing direct 

 from the germ-cells) but may be merely deviations from the 

 normal course of development, I may instance the variations 

 in the carpus recorded by Turner 1 in which the trapezium and 

 scaphoid unite, or the trapezoid and semi-lunar divide, or the 

 astragalus and navicular unite (Anderson). 



The best examples of fortuitous congenital variations arc- 

 seen in supernumerary fingers and vertebra'. The eighth 

 cervical vertebra, bearing a rudimentary rib, 2 is not a reversion 

 because the most remote ancestors of man have but seven cer- 

 vicals. In cases where a rib is developed upon the seventh 

 cervical, however, the reversion theory is perhaps applicable 

 because rib bearing cervicals are relatively less remote. The 

 same distinction applies to polydactylism. Plow absurd it is 

 to consider a sixth finger atavistic, when we remember that 

 even our Permain ancestors had but five fingers. 



We cannot, however, class as purely fortuitous a variation 

 which occurs in a definite percentage of cases presenting 

 twenty-four different varieties, but occurring in the same 

 region. Such is the much-discussed 3 musculus sternalis, a 

 muscle extending vertically over the origin of the pectoimlia 

 from the region of the sterno-mastoid to that of the ohli.pius 

 externus. Testut lightlv applies his universal reversion the- 

 ory, and as this muscle is not found in any mammal considers 

 it a regression to the reptilian presternal (Ophidia) ! Turner 

 also considered it as reversional in connection with the panm- 

 culus carnosus, the old twitching muscle of the skin which 

 plays so many freaks of reversion in the scalp and neck ; this 



'Journal of Anatomy and Physiology, 1884, p. 245. 



*Arb. Lane : Journal of Anatomy and Physiology, 1885, p. 266. 



'See T„rn. r Sh.nherd. and Cunningham : Journal of Anatomy and Phys.ology. 



