286 A MANUAL OF PHYSIOLOGY 



other parts of the alimentary canal. It is far more closely 

 related to the central nervous system, and, unlike the 

 peristaltic contraction of the intestine, can pass over any 

 muscular block caused by ligature, section, or crushing, so 

 long as the nervous connections are intact. But division 

 of the cesophageal nerves causes, as a rule, stoppage of 

 cesophageal movements ; although under certain circum- 

 stances an excised portion of the tube may go on contract- 

 ing in the characteristic way after removal from the body. 

 Again, the peristaltic wave when artificially excited seems 

 always under normal conditions to travel down the oesophagus, 

 never to spread upwards or in both directions, as may 

 happen in the intestine. Stimulation of the mucous mem- 

 brane of the pharynx will cause reflex movements of the 

 oesophagus, while stimulation of its own mucous membrane 

 is ineffective. From these facts we learn that although the 

 muscle of the oesophagus may possess a feeble power of 

 spontaneous peristaltic contraction, yet this is usually in 

 abeyance, or at least overmastered by nervous control ; so 

 that impulses, passing from a nerve centre and travelling 

 down in regular progression along the cesophageal nerves, 

 excite the muscular fibres in succession from the upper to 

 the lower end of the tube. 



The centre for the whole involuntary stage (both pharyn- 

 geal and cesophageal) of deglutition lies in the upper part 

 of the medulla oblongata. When the brain is sliced away 

 above the medulla deglutition is not affected, but if the 

 upper part of the medulla is removed, the power of swallow- 

 ing is abolished. In man disease of the spinal bulb interferes 

 far more with deglutition than disease of the brain proper. 



Normally the afferent impulses to the centre are set up by 

 the contact of food or saliva with the mucous membrane of 

 the posterior part of the tongue, the soft palate and the 

 fauces, the nerve-channels being the superior laryngeal, the 

 pharyngeal branches of the vagus, and the palatal branches 

 of the fifth nerve. A feather has sometimes been swallowed 

 involuntarily by a reflex movement of deglutition set up 

 while the soft palate or pharynx were being tickled to 

 produce vomiting. Artificial stimulation of the central end 

 of the superior laryngeal will cause the movements of degluti- 



