236 



CONDITIONS INFLUENCING THE INTESTINAL MOVEMENTS. 



the fibres of both levatores converge below, and become united with the fibres of 

 the external sphincter, they aid the latter, during energetic contraction of the 

 sphincter ; or, as Hyrtl put it, the levatores are related to the anus, like the two 

 cords of a tobacco pouch. During the periods between the evacuation of the gut, 

 the faeces- appear only to reach the lower end of the sigmoid flexure. As a rule, 

 from thence downwards, the rectum is normally devoid of faeces. It seems that 

 the strong circular fibres of the muscular coat, which Nelaton has called sphincter 

 ani tertius, when they are well developed, contract and prevent the entrance of 

 the faeces. When the tendency to the evacuation of the rectum is very pressing, 



Auerbach' s plexus shown in section (human), a, ganglionic cells ; b, nerve fibres ; 

 c, section of the circular muscular fibres ; d, longitudinal muscular fibres. 



the anus may be closed more firmly from without, by energetically rotating the 

 thigh outwards, and contracting the muscles of the gluteal region. 



161. CONDITIONS INFLUENCING THE INTESTINAL MOVEMENTS. 



The intestinal canal contains an automatic motor centre within its walls, the 



Fig. 175. 

 Plexus of Auerbach, prepared from the small intestine of a dog, by the action of gold chloride. 

 The nerve-cells are shown at the nodes, while the fibrils proceeding from the ganglia, and 

 the anastomosing fibres, lie between the muscular bundles. 



plexus myentericus of Auerbach which lies between the longitudinal and circular 

 muscular fibres of the gut. It is this plexus which enables the intestine, when cut 

 out of the body, to execute, apparently spontaneously, ' movements for some time. 



