Wrinkles form in the dermis.
The dermis is the thick layer of living tissue below the epidermis that forms the "true skin", containing blood capillaries, nerve endings, sweat glands, hair follicles, and other structures.
In briefest summary, the dermis is:
DERIVATIVES
Dermal (adjective)
Dermic (adjective - rarely used).
ORIGIN
Mid 19th Century.
Modern Latin, suggested by epidermis.