44 HORSESHOEING. 



(4) bulbar venous plexus (Fig. 26, B). All these plexuses of 

 small veins contribute to form the digital veins (Figs. 25 and 

 26, A), 



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 iti the soft tissues just 

 under the homy 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- 

 sl'in (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 Tvdth 

 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 con- 

 nective tissue. 



