458 MOVEMENTS OF (ESOPHAGUS. [BOOK n. 



nervous tracts to successive portions of the organ. If the oesophagus 

 be cut across some way down, or if a portion of the middle region 

 be excised, stimulation of the pharynx will produce a peristaltic 

 contraction, which travelling downwards will not stop at the cut 

 or excision but will be continued on into the lower disconnected 

 portion by means of the central nervous system. And it is stated 

 that ordinary peristaltic contractions of the lower part of the 

 oesophagus can be readily excited by stimulation of the pharynx, 

 but not by stimuli applied to its own mucous membrane. In 

 the reflex act which thus brings about the- peristaltic contraction 

 of the oesophagus the afferent nerves are those of the pharynx, 

 vix. the superior laryngeal nerve and pharyngeal branches of 

 the vagus, branches of the fifth, and in some animals at least 

 branches of the glossopharyngeal, but chiefly the first; and 

 cesophageal movements can easily be excited by centripetal 

 stimulation of the superior laryngeal. The centre lies in the 

 medulla oMongata, being a part of the gem-nil deglutition 

 centre ; and the efferent impulses pass along fibres of the vagus, 

 reaching the upper part of the oesophagus by the recurrent 

 laryngeal nerves and the lower part through the cesophageal 

 plexuses of the vagus (Fig. 70). Section of the trunk of the vagus 

 renders difficult the passage of food along the oesophagus, and sti- 

 mulation of the peripheral stump causes cesophageal contractions. 



The force of this movement in the oesophagus is considerable ; 

 thus in the dog a ball pulling by means of a pulley against a 

 weight of 250 grammes has been found to be readily carried down 

 from the pharynx to the stomach. 



At the junction of the oesophagus with the stomach the circular 

 fibres usually remain in a more or less permanent condition of 

 tonic or obscurely rhythmic contraction, more particularly when 

 the stomach is full of food, and thus serve as a sphincter to 

 prevent the return of food from the stomach into the oesophagus. 

 Upon the arrival of the bolus of food at the end of the oesophagus, 

 the centre for this sphincter is inhibited and the orifice is thus 

 opened up. Possibly the patency of the orifice is still further 

 secured by a contraction of the longitudinal muscular fibres which 

 radiate from the end of the oesophagus over the stomach. 



271. Movements of the Stomach. While the object of the 

 cesophageal movement is simply to carry the swallowed bolus with 

 all due speed to the stomach, and while the intestinal movement 

 has, in like manner, simply to carry the intestinal contents 

 onward, the twisted course of the looped path ensuring all the 

 mixing of t>he constituents of the contents that may be necessary, 

 the movements of the stomach have a double object : on the one 

 hand to provide an adequate exposure of the contents of the 

 dilated chamber to the influence of the gastric juice, and on the 

 other to propel the partially digested food, when ready, into the 

 duodenum. We may accordingly distinguish between what we 



