=Nerves= are roundish white cords which come from the brain and spinal cord; they generally accompany arteries. They divide and subdivide into smaller and smaller branches till they become invisible to the naked eye and are lost in the tissues. The nerves that are found in the foot come from the spinal cord, and because the largest nerves of the foot accompany the digital arteries they are called _digital nerves_ (Fig. 25, 1). The branches ramify throughout all parts of the foot except the horny box and the hair. Nerves, according to their use or function, are classed as _motor_ and _sensory_. The motor nerves end in muscles which they stimulate to action and control. The sensory nerves terminate in the skin and in the soft tissues just under the horny box or hoof (pododerm), and render these parts sensitive; that is, they convey certain feelings, as, for example, the pain caused by bruising, pricking, or close-nailing, to the brain and consciousness. F. The Protective Organs of the Foot. The protective organs are the skin and the horny box or hoof. The _external skin_, or _hide_, covers the entire body; in the feet it covers the bones, tendons, and ligaments, even passing in under the hoof and directly covering the os pedis. This portion of the skin, enclosed by the hoof and therefore invisible, is called the _pododerm_ or foot-skin. In Germany it is called the _hoof-skin_ (huflederhaut), because it is a continuation of the outer visible skin, and because it secretes the hoof,—that is, the hoof is produced by it. That part of the skin which is covered with hair is known as the external or _hair-skin_. (_a_) =The hair-skin= (Fig. 27, _a_) consists of _three_ superposed _layers_,—(1) the _external_ superficial layer, or _epidermis_; (2) the _middle_ layer, _derm_ or leather-skin (so-called because leather is made from it); (3) the _internal_ layer, or _subcutaneous connective tissue_. 1. The _external layer_, or _epidermis_, is composed merely of single flattened, horn-like cells (scales) lying side by side and over one another, and uniting to form one entire structure,—a thin, horn-like layer, without blood-vessels or nerves. It extends over the entire surface of the body, and protects the underlying, very sensitive middle layer from external influences. The oldest cell-layers lie on the outer surface, and are being continuously brushed off in patches or scales, while new ones are constantly being formed on the outer surface of the middle layer.