66 DIGESTION. 



powerful in carnivora, and very effective also in herbivorous 

 quadrupeds. 



In the latter we observe a lateral movement which the 

 French have called " mouvement de diduction," and which 

 really is the movement of the axis of the lower jaw across 

 that of the upper. It is rather a rotatory movement than a 

 lateral displacement, one of the articulatory heads of the 

 lower jaw being fixed or turning on its own centre, whilst 

 the opposite one describes an arch. The nature of this lateral 

 movement explains how it can only occur one way at a time, 

 as Colin has shown by some very interesting experiments. 



All the organs of mastication act with a remarkable regu- 

 larity in herbivorous animals, and we find that the movement 

 of the lower jaw may persist from one side to the other, 

 whichever it may be, for a quarter of an hour, and even for 

 one whole hour at a time. Thus the lower jaw may move 

 to the right and back to the left, the grinding process going 

 on between the right molars, and vice versa. This unilateral 

 movement, Colin says, may be observed in the horse, ass, 

 mule, deer, hemione, zebra, rhinoceros, ox, buffalo, bison, an- 

 telope, sheep, goat, and other ruminants. 



In all herbivorous animals mastication is slow, and Colin 

 has found that, on an average, a horse requires an hour and 

 a quarter to eat four pounds of hay, and of which, in chewing, 

 he makes from sixty to sixty-five boluses. The process of 

 mastication is much favoured by the flow of saliva, and the 

 movements of the jaw are more numerous when this is 

 scanty. 



The slow act of chewing in the horse is destined for the 

 complete trituration of food which has to pass quickly through 

 the stomach. The act of mastication and insalivation is more 

 essential in the horse than in omnivorous or carnivorous 

 animals, and if oats are passed through the mouth uncrushed, 



