There are two layers of membrane composing the skin—the _cutis vera_, dermis, or true skin, which is the inner portion; and the cuticle, epidermis, or scarf-skin, which is the outside layer. The dermis, or true skin, consists mainly of a net-work or web of fibrous material, having outside of this a net-work of capillary blood-vessels and lymphatics, interwoven with still another net-work, of nerves, both blood-vessels and nerves terminating in projecting or upright loops, each loop formed of a blood-vessel and a nerve-cord, the two being together side by side. These loops, which are the most extremely sensitive portion of the skin, are called _papillæ_, and they form the projecting fine ridges that are seen on the palm of the hand, where their abundance gives the hand its superior sense of feeling or touch. All these parts—the fibrous meshes, the blood-vessels, nerves, and loops of papillæ—are microscopically minute. The outside skin or cuticle has no blood-vessels or nerves, and hence no life or sensation, but seems to be a _covering_ to protect the true skin, and to modify or diminish its otherwise too extreme sensitiveness; besides being of use in other ways to the general system. It is that part which is raised up when a blister is produced; and the sensitiveness of the papillæ under it, where it is taken off, shows its necessity. The matter of which it is formed is secreted or poured out by the true skin, and is the same matter which, when dried and hardened in various degrees, becomes the thick skin on the sole of the foot, the callous place on the hand or elsewhere, the dandruff of the head, the hair on any part of the body, the nails of fingers and toes, the hard portion of warts, and the hard or soft corn. All these are essentially the same thing under different modifications. It is constantly worn off from the external surface, and as constantly added to at the under side. This internal or under-side layer of the cuticle is commonly distinguished as the _rete mucosum_, and contains a colouring matter secreted from the true skin, which, as it is greater or less in quantity gives the different shades of complexion; the semi-transparent nature of the matter outside allowing it to show through. The oil tubes and perspiratory ducts take their rise immediately under the skin, and find their way to the surface, while nerves and blood-vessels traverse it forth and back. Some further idea of the nature of the skin may be gained by observing a piece of thick sole-leather in which that part called the grain is the cuticle or epidermis, and the thicker portion is the dermis, or _cutis vera_.