PATHOLOGY

Detailed explanation-1: -Spines are the stiff, enlarged guard hairs that exhibit definitive growth and form the protective quills of echidnas, hedgehogs and especially porcupines.

Detailed explanation-2: -There are three major components to a guard hair: the outer layer, called the cuticle; the middle layer, called the cortex; and the inner layer, called the medulla. The cuticle has a variable scale pattern, the cortex contains the pigment of a colored hair, and the medulla ranges from absent to very complex.

Detailed explanation-3: -Coarse, hollow, dark guard hairs cover soft, woolly underfur. Guard hairs can absorb solar energy and help reduce energy expenditure. But their primary function is to protect the underfur. Long and waterproof, guard hairs channel moisture away from the underfur and skin.