70 THEORY OF FEEDING. 



bladder), ureters (two tubes which convey urine from the 

 kidneys to the bladder), and interior of the eyes and eyelids. 

 It is continuous with the skin, and the skin is continuous with 

 the membrane that secretes the hoof. We may regard the 

 mucous membrane as a modification of the skin, from which 

 it differs with respect to its structure only in its being thinner and 

 softer. The mucous membrane of the stomach and intestines 

 is provided with a great number of minute vessels, called 

 absorbents. The membrane which secretes the hoof may also 

 be looked upon as a modification of the skin. The structure 

 known as skin is composed of a secreting surface (the true skin) 

 and a covering surface (epidermis, page 18), which consists 

 of more or less horny scales secreted by the true skin, and 

 which is more or less impermeable to fluids. The mucous 

 membrane secretes mucus, which is a slimy and semi-fluid 

 substance, as we may see from an inspection of phlegm, or of 

 discharge from the nose. The three surfaces in question pos- 

 sess strong mutual sympathy. Thus, in catarrh for example, 

 the coat loses its polish, and the intestines become irritable ; 

 during an attack of indigestion, the condition known as " hide- 

 bound " is often present ; and laminitis (inflammation of 

 the feet) may arise from superpurgation. On the other hand, 

 a soft, glossy coat is an indication that the organs of breathing 

 and digestion are in good order. 



At the beginning of the alimentary canal we have the lips, 

 mouth, and gullet, which, at its entrance into the stomach, is 

 constructed so as to render vomition extremely difficult. 



The horse's stomach has an average capacity of about 3j^ 

 gallons, and is provided with a large number of glands which 

 supply it with gastric juice, and which are found only on about 

 one-half of the interior surface of that organ ; the other half 

 being merely a continuation of the gullet. Hence the size of 

 the functional stomach is only about half that of the apparent 

 one. 



