THE SKIN OR INTEGUMENT. 727 
It was formerly thought that the nerve fibrils were directly continuous with the 
central ends of the gustatory cells, but this view is no longer entertained. 
The ducts of Ebner’s glands open into the bottom of the valleys surrounding 
the papille vallate, and the serous-like secretion of these glands probably washes 
the free hair-lke extremities of the gustatory cells, and so renders them ready to 
be stimulated by successive substances. It should be added that there is a close 
association between the senses of smell and taste. This can be best appreciated by 
considering the defective taste perceptions resulting from inflammatory conditions 
of the nasal mucous membrane or the common practice of holding the nose in 
order to minimise the taste of nauseous drugs. 
THE SKIN OR INTEGUMENT. 
ORGANS OF TOUCH. 
THE SKIN. 
The skin (integumentum commune) covers the body, and is continuous, at the 
orifices on its surface, with the mucous lining of its alimentary and other canals. It 
contains the peripheral terminations of the sensory nerves, and serves as an organ 
of protection to the deeper tissues. It is the chief factor in the regulation of the 
body temperature, and by means of the sweat and sebaceous glands, which open on 
its free surface, constitutes an important excretory structure. Its superficial layers 
are modified to form appendages in the shape of hairs and nails. 
The superficial 
area of the skin 
averages about one 
and a-half square 
metres, whilst its 
thickness varies 
Duct of ; 
sweat gland ; He 
Epidermis 
Hair 
from 0°5 to4 mm., 
being greatest Ora ey ints of 
the palms of the coriun 
hands and_ soles 
of the feet, and — sebaceous 
on the back of Soni 
the neck and 
shoulders, and Erector | 
least on theeyelids | Y. 
aud penis. It is : 
very elastic and Mair follicle X 
resistant, and its , 
colour, determined 
partly by its Ne Glomerulus 
pigment and of sweat 
partly by that of ean 
the blood, is deeper 
on exposed parts 
and in the regions 
of the genitals, - 
Subeutaneons fatty tissue 
axille, and mam- < 
mary areole, than OSD 
elsewhere. The ; rida i | Oblique section through 
colour also varies Papilla of hair a Pacinian corpuscle 
with race and age, 
the different races (ray 
of the world being roughly classified, according to the colour of their skin, into 
the three groups of white, yellow, and black Pinkish in colour in childhood, the 
Fig. 536.—VERT:CAL SECTION OF THE SKIN (schematic). 
