| The glands discharge their contents by the contraction of the arrector pili muscle and by any pressure applied to the gland. |
| A small muscle, the arrector pili, is attached to each hair follicle, with the exception of the small follicles that produce only fine vellus hairs. |
| They also lack arrector pili, so their fur can be streamlined as they swim. |
| At the hair follicle, one or several sebaceous glands and an arrector pili muscle, which causes the hair to stand on end, can be found. |
| The structure consisting of hair, hair follicle, arrector pili muscles, and sebaceous gland is an epidermal invagination known as a pilosebaceous unit. |
| Associated with the follicle are sebaceous glands and the arrector pili smooth muscle fiber bundle. |
