Three layers of dead cells compose the shaft of a hair. The outer layer, called the cuticle, consists of flattened cells that are known as cuticular scales. Beneath the cuticle lies the cortex, a layer of tightly packed, cigar-shaped cells. The core of the shaft, called the medulla, is made up of loosely packed, boxlike cells. Glands and muscles.
Most hair follicles contain an oil gland called the sebaceous gland.
This gland secretes oil into the follicle. The oil flows over the hair, lubricating it and keeping it soft. A muscle known as the arrector pili is attached to most hair follicles. In mammals with heavy coats, hair in this position traps air close to the animal's body, providing extra insulation against the cold. Hair standing on end also makes an animal look larger and more dangerous.