CRANIAL NERVES AND SENSE-ORGANS 253 



as special organs of touch in Vertebrates the tactile cells in the 

 deeper layers of the Rete Malpighii which occur in the tip of 

 the pig's snout and the bill and tongue of birds ; the touch 

 corpuscles in the skin-papillae of man and apes, and the Vater- 

 Pacinian corpuscles in the sub-epithelial tissue of the palm and 

 sole and joints of man, in the skin of the elephant, the bat and 

 many other animals, in the mesentery of the cat, in the mucous 

 membrane of the intestines, the genitals and the ball of the 

 foot of carnivora, and in the hoof of the horse and sheep. 

 Another species of tactile nerve-ending is seen in Krause's end- 

 bulbs in the lips, tongue and palate of mammals, and here and 

 there in the ball of the foot in carnivora. The ramifications of 

 the nerve-plexus in the cornea form another variety of nerve- 

 ending, and lastly many mammals possess extraordinary sensi- 

 tive tactile organs in their whiskers, which are connected with 

 nerves and can be moved by voluntary muscles. These hairs 

 are very strong and bristly. It would be incorrect to describe 

 such " sensory hairs" as peculiar to animals, for the hair of the 

 head and the beard in man, as well as the downy hairs on 

 a woman's skin, are undoubtedly keenly sensitive to the slightest 

 touch. 



Tactile sensation in man is most acute at the tip of the 

 tongue, sixty times more so than in the upper arm, thigh and 

 back. This sense of touch is the foundation of a cutaneous 

 sense of space, by means of which, without the aid of the eye, 

 the size, shape and length of an object can be determined by 

 feeling its sides, not merely by touching the object but by feeling 

 it all over (e.g., with the hands of the ape, the elephant's trunk, 

 the tongue of every animal, the upper lip of ungulates, the 

 feelers of insects). 



Just as the extreme tactile sensibility in the sole of the 

 human foot is of the utmost importance to a sure gait, so all 

 animals, in spite of their horny feet or hoofs, enjoy perfect sen- 

 sation as to the nature of the ground on which they stand or 

 move. 



Pressure-sensibility as a special cutaneous perception is, 

 according to Goldscheider, not associated with the same skin- 

 areas or nerve-endings as the sense of touch. 



In man the parts of the skin most sensitive to pressure are 



