皮層 is read as ひそう (hisou) and means cortex.
ひそう
hisou
かわ
mask (hiding one's true nature)
ひにく
(only) surface
ひふ
skin
かわきり
beginning
ひふびょう
skin disease
ひかく
leather
かわざんよう
over-optimistic calculation
ひふか
dermatology
ひか
subcutaneous
ひしつ
cortex
ひにくる
to make a cynical remark (about)
ひし
sebum