216 THE HUMAN SPECIES 



When we come to consider the actual process of digestion 

 we find in the first place that the alimentary canal is the longer 

 and the act of digestion the more complex according as the 

 diet contains more vegetable food. 



LENGTH OF ALIMENTARY CANAL. 



In carnivora : lion, tiger 3 times the length of the body 



dog 5 



omnivora : chimpanzee 6 ,, 



man 7 



herbivora 1 1-26 



Herbivora and omnivora drink fluids by sucking, carnivora 

 by lapping them with the tongue. 



Carnivora take their solid food in great lumps which they 

 tear off and bolt whole ; omnivora and herbivora chew their 

 food, mixing it with saliva before swallowing it. 



In mastication the up and down movement is produced by 

 the masseter, temporal and internal pterygoid muscles acting 

 simultaneously ; the side to side chewing of ruminants is pro- 

 duced by the alternate action of the external pterygoid of one 

 side and the masseter of the other ; in chewing backwards 

 and forwards like rodents both external pterygoids work to- 

 gether. 



In man the peculiar conformation of the articular head of 

 the lower jaw allows of all three movements. 



The saliva, which contains a diastase capable of converting 

 starch into dextrine and sugar, plays an important part in 

 digestion ; this is most marked in man, apes, pigs and rodents ; 

 the saliva of horses, oxen and sheep is very feebly diastatic ; 

 that of carnivora and bears (omnivora) is practically inert. As 

 regards the amount of salivary secretion, it is greatest in herbi- 

 vora and least in carnivora. Ellenberger l gives the following 

 table of amounts secreted in twenty-four hours : 



Man 200-2,000 gm. 



Horse 10-40 kilogm. 



Ox 50 



Dog about TOO- 1 20 gm. per hour 



1 Ellenberger, loc. cit., ii., p. 511. 



