THE DIGESTION OF THE FOODSTUFFS 139 



a sling around the rectum. During defaecation the tonus of 

 the sphincters is inhibited, thus allowing the faeces to pass 

 out. The defaecation is produced by the peristalsis of the 

 rectum, aided by abdominal pressure. The muscles produc- 

 ing this pressure are the diaphragm and the muscles of the 

 abdominal walls. 



The centre of defaecation is situated in the lumbar cord. 

 It is stimulated reflexly from the rectum. The inauguration 

 of the reflex depends, to a certain extent, upon the will. 

 The nerves going from the centre to the muscles of the 

 rectum run through the hypogastric plexus and the sympa- 

 thetic (ganglion mesentericum posticus) and the nervi 

 erigentes. The first-named nerves are supposed to be motor 

 nerves for the circular muscles and inhibitory nerves for the 

 longitudinal muscles; the last-named are supposed to be 

 motor nerves for the longitudinal muscles and inhibitory 

 nerves for the circular muscles. 



Defaecation takes place in man at least once a day. 



