STRUCTURE OF THE SKIN. 85 
This villous surface is observable on the skin, in almost 
all quadrupeds. It is found in the soles of the feet only, in 
birds and reptiles. In fishes and the inferior animals, its ex- 
istence has not been satisfactorily ascertamed. 
The corium may be observed in quadrupeds, birds, rep- 
tiles and fishes. It is less distinct in the mollusca and crus- 
tacea; and in the animals of the lewer orders, it has not 
been detected. 
Irom the experiments which have been made, to ascer- 
tain the composition of the cortum, it appears to consist 
chiefly of gelatine. Hence it is that part which is employ- 
ed in the manufacture of glue. In the thin, soft, flexible 
hides, the gelatine dees not possess the same degree of vis- 
cidity, as in those of more rigid texture; and the glue ob- 
tained from such, is proportionally weak. 
It has already been stated, that gelatine unites with tan- 
nin, forming a substance which is insoluble in water. It 
is to this combination that /eather owes its peculiar proper- 
ties. The skin is prepared for being converted into leather, 
by maceration in water or lime-water, in order to remove 
the cuticle and hairs. ‘The tannin is obtained from oak-bark, 
by infusion in water. The cleansed skin, now consisting 
chiefly of gelatine, upon being placed in this infusion, 
unites with the tannin. The strength of the leather de- 
pends on the strength of the hides; the more rigid these 
are, the more tough and durable is the leather which they 
furnish. 
4. Muscular web— This is likewise termed Panniculus 
curnosus. It varies greatly m its appearance according to 
the motions which the skin and its appendices are destined 
to perform. It consists of a layer of muscles, the extremi- 
ties of whose fibres are inserted into the corium externally, 
and adhere to the body iternally in various directions. 
This layer is very obvious, i the hedgehog and the pereu- 
