564 THE MECHANICAL PROCESSES OF DIGESTION [CH. XXXVII. 



levator ani and external sphincter are concerned, and the paralysis 

 of these voluntary muscles may lead to incontinence of faeces. 



We thus see that the lowermost portion of the alimentary canal 

 resembles its uppermost portion (pharynx and oesophagus) in being 

 more under external nervous control than is the small intestine. 

 Autonomy at the rectal and anal portion is for obvious reasons unde- 

 sirable. 



