350 



VIERISTIC VARIATION. 



[PART i. 



. P.ut in a large majority of -ases of the presence of an extra 

 n tin- radial side, the thumb has two phalanges as usual. Upon 

 i review of the evidence it is I think clear that we shall In- right in 

 considering th.-it iii mosl <>f these cases the extra digit is not really in 

 Succession to the thumb, but that tin- two radial digits together rep re - 

 -ent tin- thiinili, tin- increase in number being achieved by duplication 

 and not by siicces-ive addition. 



.Must authors (GRUBEBj &c.) thus speak of these formations as 

 double-thumb- and recognize them as examples of duplicity, but it 

 -hould be remembered that tin- \ie\v of their nature is not consistent 

 \\ith any statemenl that either of the t\vo digits is the extra one. If 

 these thumb-' are instances >f duplicity then both together represent 

 t IK- normally single t liumb. 



In clear cases of double-thumb the two thumbs are equ'al or nearly 

 eimal in si/.e and development, as commonly happens in cases of true 

 duplicity. I>nuble-thumbs are known in every degree of completeness. 

 The division between the two may occur at any point in their length. 

 Thus the duplicity may be confined to the nail and first phalanx 

 ITTO, .!///>//. sexc. 1><. "'/(/>., Taf. xxv. tig. 1; BIKXKAUM, Monatsschr. 

 i. f.'Jin //>/.-., I860, xvi. p. Hi"); or it may include both first and second 

 phalanges ((Jiiri'.KR, Arch. f. path. Anat. Phys., xxxn. 1865, p. 223); or 

 both phalanges and the greater part of the metacarpal (GAILLARD, 

 MI' in. Soc. de liol., 1^(31, p. 325); or even the whole digit and meta- 

 carpus, the two thumbs separately articulating with the trapezium 

 f .losKi'ii, quoted by <ii;rBER, I.e., p. 463, Xote 37). It would be 

 interesting to know which of these conditions is the most frequent, for 

 it is likely that between the degrees of this variation there is Dis- 

 continuity, but the point is not easy to determine. As regards records 

 the conditions first and last named are much the rarest, and the double- 

 thumbs \\ith two sets of phalanges articulating with one metacarpal 

 constitute the majority of cases. 



Sometimes the two thumbs are webbed together (GRUBER, Bull. Ac. 

 Sci. 1'i't. xv. p. 4SO, fig.) sometimes they are separate and may be 



YH-. 101. Hight hand having a thumb double from the metacarpus, shewing the 

 relationship of images bot\\xrn the two thumbs. (After AXSAXDALE.) 



