DEEMATOGLYPHICS IN PRIMATES 157 



Kolossof and Paukul ('06) analyzed ridge direction on a 

 mathematical basis, pointing out that observed ridge directions 

 are in keeping with the mechanical conditioning described by 

 Kollmann. 



Cummins and Sicomo, and Cummins ('26), resort to the 

 observation of dermatoglyphics in developmental defects of 

 human hands and feet as a substitute for experimental analy- 

 sis of the factors which condition ridge direction. The material 

 includes cases of syndactyly, polydactyly and other more 

 grave involvements of form of the members. The cogent 

 elements of the evidence and the main conclusions are : 



1 'The causation of ridge direction, hence the source of aber- 

 rant configurations in the abnormal material, is suggested 

 when from case to case it is found that the normal plan of 

 configurations undergoes a marked modification or is even 

 suppressed. It would appear that there are no predetermined 

 limits to the potencies of ridge direction, actual expression 

 of ridge direction being dependent in some manner upon 

 factors which are causally related to the formation of contours. 



Form (contour; relief) connotes differential growth, and 

 the control of ridge alignment must be exercised by growth 

 of the parts during the period of ridge differentiation. ' ' 



Bonnevie ('24), on the basis of the digital distribution and 

 inheritance of finger-tip patterns as well as five cases of 

 polydactyly, also concludes that there is probably a causal 

 relationship between the form of the apical pads of the fetal 

 digits and their ridge configurations. Further studies by 

 Bonnevie ('27, '29, '31 and '32), Cummins ('29), Schaeuble 

 ('33) and Abel ('35, '36 and '37) have extended the informa- 

 tion on embryogenesis of dermatoglyphic patterns, but for 

 the present purpose only the immediately relevant generaliza- 

 tions need be given. 



In the human fetus the critical period of ridge differenti- 

 ation is in the third and fourth months. Epidermal ridges 

 are not formed simultaneously over the whole palmar and 

 plantar surfaces, nor, according to work now in progress 

 (Cummins), are the hand and foot synchronous in ridge de- 



