CHAPTER XVIII. 



ARRANGEMENT OF THE PAPILLARY RIDGES. 



The subjects of the preceding, present, and the succeeding 

 chapter are closely allied, from the fact that they all deal with 

 structural changes in the mammalian skin, and that most of these 

 are exhibited for us on our own palms and soles. They certainly 

 comply "with the canons of Henri Poincare as to simplicity, regularity 

 and chance of recurring. 



In the last chapter, papillary ridges as organs of touch were 

 briefly referred to, but their mode of development into complicated 

 patterns do not concern the questions here at issue. The general 

 manner in which they are arranged on the hands and feet of man 

 and the Primates below him is very much a matter for such Larnarc- 

 kian methods of inquiry as I have chosen. In this examination 

 of the ridges I will proceed from man backwards among the Primates 

 and lower still. I described these ridges, in a book previously 

 referred to in the following words, and find no need to alter them 

 here. : ' The ridges and adjoining furrows which cover the palmar 

 and plantar surfaces of all Primates and a few lower forms in smaller 

 degree, may be compared to the ridges of a ploughed field over 

 which some object, as a light roller, has been passed, the effect of 

 this being to produce a series of ridges with flattened tops. This 

 can be well seen with a lens when the ridges are examined in profile, 

 and is their normal condition in man and many lower animals, 

 in nearly all the palmar, plantar and digital regions." 1 The reserva- 

 tion in the last sentence is not material here. 



The Hand of Man. 



Beginning with the tips of man's fingers and excluding the 

 wonderful patterns which Galton did so much to elucidate and 

 bring into order, we find the ridges are placed, to a remarkable 

 extent, parallel with the skin-flexures which will be treated in the 

 next chapter. I term the thumb and fingers D 1, 2, 3, 4, 5 for the 

 sake of accuracy (Fig. 59). Over the last joints (distal) of all the 

 digits the ridges suddenly diverge from their directions in the 

 patterns of the pulps, and become arranged transversely to the 



1 Sense of Touch in Mammals and Birds. 



