COMPARATIVE ANATOMY. 153 



ed, and which are very great, the organs of taste and smell- 

 ing are situated near each other. 



III. To the mouth adjoins the gullet : in this part also, 

 comparative anatomy discovers a difference of structure, 

 adapted to the difierent necessities of the animal. In brutes, 

 because the posture of their neck conduces little to the pas- 

 sage of the ahment, the fibres of the gullet which act in this 

 business run in two close spiral lines, crossing each other ; 

 in men, these fibres run only a little obliquely from the 

 upper end of the oesophagus to the stomach, into which, by 

 a gentle contraction, they easily transmit the descending 

 morsels : that is to say, for the more laborious deglutition of 

 animals which thrust their food up instead of dow7i, and 

 also through a longer passage, a proportionably more power- 

 ful apparatus of muscles is provided — more powerful, not 

 merely by the strength of the fibres, which might be attrib- 

 uted to the greater exercise of their force, but in their collo- 

 cation, which is a determinate circumstance, and must have 

 been original. 



IV. The gullet leads to the intestines: here, likewise, 

 as before, comparing quadrupeds with man, under a general 

 similitude we meet with appropriate differences. The val- 

 vulcB conniventeSy or, as they are by some called, the semi- 

 lunar valves, found in the human intestine, are wanting in 

 that of brutes. These are wrinkles or plates of the inner- 

 most coat of the guts, the effect of which is to retard the 

 progress of the food, through the alimentary canal. It is 

 easy to understand how much more necessary such a provis- 

 ion riiay be to the body of an animal of an erect posture, 

 and in which, consequently, the weight of the food is added 

 to the action of the intestine, than in that of a quadruped, in 

 which the course of the food, from its entrance to its exit, is 

 nearly horizontal ; but it is impossible to assign any cause 

 except the final cause, for this distinction actually taking 

 place. So far as depends upon the action of the part, this 

 structure was more to be expected in a quadruped than in 



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