TOUCH 
27 
numerous touch-corpuscles which underlie the little ridges seen 
on the tips of our fingers and thumbs (fig. 1032). 
Birds, and Mammals there are also curious struc- 
tures known as Pacinian bodies (fig. 1033), in 
which the ending of a nerve is surrounded by a 
series of layers arranged almost like the coats of 
an onion. There is reason to think that these are 
very sensitive to slight pressures. They abound, 
for instance, in the wing-membranes of Bats, and 
it is well known that these creatures can easily 
steer their way in the dark through a veritable 
maze of obstacles, such as that afforded by a 
series of strings running in various directions. 
Pacinian bodies are also found connected with 
tendons, ligaments, and various internal organs. 
In Reptiles, 
aa 
ane 
Fig. 1032. — Touch- 
Corpuscle from Finger 
Tip of Man, in section, 
greatly enlarged 
The use of these is probably to apprise the central nervous 
system of variations in pressure and tension which take place 
as between the different parts of the body 
itself. 
We are still very much in the dark as 
to how far there do or do not exist special 
end-organs which are affected by variations 
in temperature. It is known that definite 
spots in the human skin are sensitive to 
such variations, but there do not appear 
to be any special sense-organs in these 
spots. Some of the sensory nerve-fibres 
terminate in the skin by dividing into a 
number of little branches which do not 
YH $i 
become continuous with modified epidermal NS 
cells, and it has been suggested that these 
“free nerve endings” are related to the H, 
Fig. 1033.—A Pacinian Corpuscle 
temp erature sense. in Longitudinal Section, enlarged. A 
While the entire external surface of the sets (ea ines oy 
sheat , enters the base o 
body 1s sensitive to contact, pressur e, and corpuscle, loses its sheath, traverses 
a central core (7), and ends in an 
changes in temperature, this is 10. ANY cesar expansion Ga). ‘The cor 
puscle is mostly made up of numerous 
cases insufficient to enable the requisite ree ee ebrous layers le, 4). 
adjustments to the environment to be 
brought about. And we accordingly find that in many animals 
organs of active touch have been evolved, which explore the 
