446 Duplicate Twins and Double Monsters 



and left hands either of the same individual or one of x and one of y, 

 are also exact symmetrical equivalents. The exception just mentioned 

 is hard to find and is so slight that I was for a long time in doubt 

 whether or not to express it in the formulae as given in the list on 

 page 436. As may be clearly seen by consulting the formula, it is found 

 at the origin of line D in the left hand of y, where by a slight differ- 

 ence in the minutis of the ridges, the line arising from the 4th digital 

 triradius cannot be said strictly to become continuous with the 3d lower 

 triradius ( i^ ) as in a; and in both right hands. (Compare x ahd y 

 in this particular.) This case is in itself an interesting contribution 

 to the study of the ridges and their niinutioi, since it shows, as main- 

 tained elseivhere, that the exact correspondence of duplicates does not 

 extend to those latter parts save in a general way, and that a difference 

 in main line formulce often depends upon some eccentricity of a single 

 ridge, in itself sufficient to deflect the course of a line, although of no 

 importance in regard to the general pattern. Six of the eight remain- 

 ing exceptions to the correspondence of the 90 pairs of symbols em- 

 bodied in the descriptive formulce of the nine sets of duplicate twins 

 considered above are of as slight a nature, and the other two differences 

 are situated in the carpal region, and are of still less importance since 

 they are in all probability tlie result of incompleteness in the prints. 



In the ridges themselves, whether we consider their number or the 

 minutias met with along their course, we find but little similarity, 

 although more in the former than in the latter. If, for example, in 

 the two left palms of No. I (Fig. 7) fine straight lines be drawn with a 

 ruler, connecting adjacent digital triradii, and if the ridges crossed by 

 those lines be accurately counted and compared, the results are as follows: 



These differences are certainly not great, especially when we note 

 that there is often a chance for individual difference of opinion, amount- 

 ing to one or possibly two ridges each way. Thus the pencilled line 

 often crosses an interrupted line at its very end and an almost infinitesi- 

 mal difference in its position would determine whether or not that 

 line should enter the enumeration. Greater differences than this often 



