84 PHILOSOPHY OF ZOOLOGY. 
vera, or true skin. It lies immediately underneath the cu- 
ticle and mucous web. It is usually destitute of colour. It 
consistsin some animals, as quadrupeds, of solid fibres, which 
cross one another in every possible direction, and form a sub- 
stance capable of considerable extensibility and elasticity. In 
the cetacea, the fibres are arranged vertically, and exhibit an 
appearance not unlike a section of the sessile boleti. In 
fishes, it is more uniform in its texture; and in some cases 
appears a homogeneous gelatinous membrane. It is more 
obviously organized, than the two members by which it 1s 
covered. Bloodvessels and nerves penetrate its substance, 
and may be observed forming a very delicate net-work on 
its surface. 
The peripheral surface of this layer, 1s in close contact with 
the mucous web, from which it 1s with difficulty detached. 
When viewed separately, it presents numerous inequalities, 
which give to the cuticle the appearance of angular com- 
partments cn the back of the human hand, and cur- 
ved ridges on the palms. When this surface is more minutely 
examined, it appears covered with numerous tubercles, va- 
rying in shape and size according to the species or the fune- 
tions of the different parts. By maceratmg the corium for 
some days in water, the structure of these tubercles may be 
perceived. ach consists of a pencil of fibres, united at 
their base. When the central fibres are longest, the tuber- 
cle is conical ; when of equal lengths, the summit is flat. 
This portion of the corium has been characterised by a 
particular name. It is called Corpus papillare, and villous 
surface of the skin. It is most obvious in those parts 
which possess, in the greatest perfection, the sense of touch. 
It is generally supposed, that the nervous filaments, con- 
nected, with that faculty, terminate in these tubercles. They 
are depressed when not in action, but become erect on the 
application of any stimulant. 
