INVOLUTION 489 



phalangeal extremities of the fingers and toes, we would 

 state broadly that these " ridges," and their intervening 

 " furrows," while maintaining exactly the same ground- 

 plan, barring changes due to accidental alteration and 

 obliteration, alter at different periods of life in their 

 proportionate height and depth. Being intimately related 

 to the sense of touch, they change in their manner of 

 accentuation with age and occupation, being at one age 

 and another more prominent, in proportion to local 

 necessity and the special education and wants of the 

 individual, as well as in proportion to the amount of 

 peripheral nervine material deposited in, and exfoliated 

 or shed by, the digital nerve terminals. Digital ridge 

 and furrow development waxes and wanes with the 

 phenomena of systemic or organic evolution and involu- 

 tion, culminating with the attainment of the former, and 

 gradually declining with the advance of the latter, 

 showing, however, considerable divergences in incidence, 

 generally and locally, determined by general and local 

 nervine conditions and circumstances. 



These things must, therefore, be borne in mind in 

 connection with the possible medico-legal bearings of the 

 subject. Thus, in advanced life it is frequently observed 

 that the little, ring, and outer half of the middle fingers 

 show signs of effacement of the " ridge and furrow " 

 surface characters, long before the thumb, forefinger, and 

 the remaining half of the middle finger show any signs 

 of failure. The explanation of this inequality of efface- 

 ment incidence would seem to depend upon local nerve 

 distribution, along with the greater necessity for a more 

 prolonged extension of tactile acuteness by the latter 

 digits, and the consequent continuance of greater deter- 

 mination of epidermal material towards these more 

 frequently used and acutely sensitive surfaces on the 

 principle of ubi stimulus ibi fluxus proving once more 

 the truth of the contention that acuteness of innervation 

 and the maintenance of the circulation of neural pabulum 

 are always coincident and proportionate. 



In association with the incidence of "ridge and furrow" 

 effacement is atrophic change in the bulbous extremities 

 of the affected digits, whereby a more or less phenomenal 



