Associated with the hair follicle are one or more sebaceous glands. The secretions of these glands are delivered through a short duct to the space between the hair shaft and the invaginating epidermis. On the obtuse angle side between the hair root and the skin surface there is a bundle of smooth muscle fibers, known as arrector pili, attached at one end to the middle of the connective tissue sheath of the follicle, and at the other to the papillary layer of the dermis. Its contraction causes erection of the hair accompanied by the formation of "gooseflesh", and simultaneously aids in the expulsion of sebum.