20 THE SENSE OF TOUCH IN ANIMALS 



DESCRIPTION OF THE PAPILLARY RIDGES AND GENERAL 

 MODES OF ARRANGEMENT 



The ridges and adjoining furrows which cover the palmar 

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

 a smaller degree, may be compared to the ridges of a ploughed 

 field, over which some such object as a hght 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 the lower animals in nearly all the palmar, plantar 

 and digital regions. Thus the angles at which each ridge rises 

 out of its adjoining furrows are the same on both sides, but it 

 has been shown that there is a departure from this normal 

 shape of the ridges in certain regions of the hand and foot of 

 man, and occasionally in certain other Primates. This change 

 of shape I have called Imbrication of the Papillary ridges, and 

 it will be more fully described in the microscopical portion. 



The surfaces of the ridges show the openings of sudoriparous 

 glands which are plentiful wherever ridges are found. Microsco- 

 pically the ridges show abundant papillss with tactile corpuscles, 

 and these as well as the sudoriparous glands are absent from 

 the furrows between the ridges. 



The modes of arrangement of the ridges are extremely different 

 in different forms. The earhest and simplest found is that on 

 the footpads of a squirrel, in which the ridges are arranged in 

 lines radiating from the centre of a circular or nearly circular 

 eminence. A transverse arrangement is the commonest and 

 simplest of the common types, and with this may be classed 

 the oblique type. On the palm and sole many Primates have 

 the ridges arranged in a longitudinal manner. The next and 

 highest development is that in which the ridges are grouped 

 into arches, loops, elHpses and whorls. These three most 

 speciahsed forms of pattern, arches, loops and whorls, culminate 

 in the digits of man, both in the hand and foot, and in the 

 former case have received great attention from Dr. Galton, 

 forming a basis for a particular and elaborate classification of 



