•  Superficial dermis
It supports the upper portion of the hair follicles and the sebaceous glands.

•  Deep dermis
It contains the lower part of the hair follicle and the apocrine (sweat) glands.

•  Sebaceous glands
Their ducts open into the hair follicle except for the sebaceous glands located at the mucocutaneous junctions, which open on the surface of the skin (e.g. Meibomian glands).

•  Sweat glands
These are of two main types:

•  Apocrine glands are scattered throughout the haired portions of the skin. Their duct opens on the superficial portion of the hair follicle.

•  Eccrine glands are mostly located in the paw pads in dogs and cats. Their duct opens directly on the surface of the epidermis.

•  Specialized structures

•  Anal sacs are composed of:

•  Sac wall and apocrine cells in dogs. Ducts and sacs are lined by stratified squamous epithelium.

•  Sac wall, apocrine and sebaceous cells in cats. Ducts and sacs are lined by stratified squamous epithelium.

•  Perianal gland epithelial cells (also called hepatoid glands) are modified sebaceous epithelial cells. They are mostly found around the anus but also near the prepuce, on the tail, flank and groin.

•  Hair follicles
Hair follicles consist of an invagination of the epidermis into the dermis. They are responsible for the formation of the hair, which is a modified keratinized structure. They are composed of the following parts:

•  Infundibulum: superficial portion, from the epidermis to the opening of the sebaceous duct.

•  Isthmus: intermediate portion, from the opening of the sebaceous duct to the insertion of the arrector pili muscle.

•  Inferior segment: deep portion from the insertion of the arrector pili muscle to the base of the follicle.