Of all animals man has the most delicate skin: that is, if we take
into consideration his relative size. In the skin or hide of all
animals there is a mucous liquid, scanty in some animals and plentiful
in others, as, for instance, in the hide of the ox; for men
manufacture glue out of it. (And, by the way, in some cases glue is
manufactured from fishes also.) The skin, when cut, is in itself
devoid of sensation; and this is especially the case with the skin
on the head, owing to there being no flesh between it and the skull.
And wherever the skin is quite by itself, if it be cut asunder, it
does not grow together again, as is seen in the thin part of the
jaw, in the prepuce, and the eyelid. In all animals the skin is one of
the parts that extends continuous and unbroken, and it comes to a stop
only where the natural ducts pour out their contents, and at the mouth
and nails.