ANIMAL STRUCTURE AND FUNCTION. 13 



(inspiration), these expand ; the ribs are drawn outwards to enlarge the 

 chest from side to side, and the diaphragm is drawn back on each side to 

 deepen it. It is evident that this movement of the diaphragm will cause 

 considerable pressure on the liver and stomach, and if the latter is very 

 full of food, the movement will be embarrassed and carried out with 

 difficulty. It is, therefore, easy to understand why a full stomach 

 militates against fast work, which demands rapid, deep, easy respiration, 

 and also why indigestion and colic sometimes follow injudicious feeding 

 during work. 



The Belly includes the whole of that portion of the body which lies The belly, 

 below the back and between the chest and hind-quarters ; it contains the 

 stomach, bowels, liver and pancreas, i.e.^ the organs of digestion, and also 

 the spleen or milt, the kidneys and bladder, and the womb of the female. 



Digestion. — In the following account the food is traced from the Digest 



ion. 



mouth, in order to give a concise and easily understood narrative. 



Food having been taken into the mouth by means of the lips, is rolled 

 about by the tongue, chewed by the molars or grinding teeth, and at the 

 same time is mixed with large quantities of saliva which are poured out 

 from the glands behind and beneath the jaw. The quantity of saliva 

 produced is very great ; in horses or cattle always equal to or greater 

 than the amount of food consumed ; and the resulting pasty mixture 

 is carried to the back of the mouth where it enters the gullet. 



The 7nolar teeih of the horse are twenty-four in number, six on The molar 

 each side of each jaw (in advance of the first ones tiny, rudi- teeth, 

 mentary, " wolves " teeth m,ay sometimes be observed but are of no 

 importance). They present large roughened wearing surfaces, which, 

 when looked at from the front, slope downwards and outwards, leaving a 

 sharp chisel edge on the outside of the upper and on the inside of the 

 lower teeth. The teeth of the lower jaw are narrower than those in the 

 upper, and as they are moved from side to side during mastication they 

 travel over this wider surface and make very effective grindstones. 

 Whilst this movement is perfect, the teeth maintain their respective 

 contours and are worn evenly down as fast as they grow, but if the 

 lateral movement of the lower jaw is not great enough to cover the 

 entire upper surface, the sharp edges will become unduly prolonged, a Sharp 

 condition which may interfere with mastication and occasionally requires teeth, 

 removal. 



Having reached the back of the mouth the food is seized by the 

 muscles at the top of the gullet and forced down it towards the stomach. 



The gullet is situated on the left side of the lower portion of the neck The 

 and reaches from throat to stomach. Its course may be easily traced gullet. 



