484 MOVEMENTS OF (ESOPHAGUS. [BOOK n. 



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 

 cesophagus 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, chiefly 

 the superior laryngeal nerve and the pharyngeal branches of the 

 vagus ; oesophageal movements can easily be excited by centripetal 

 stimulation of the superior laryngeal ; but in some animals at least 

 branches of the fifth and of the glossopharyngeal nerves may be 

 so employed. The centre lies in the spinal bulb, being a part 

 of the general deglutition centre. The efferent impulses pass 

 along fibres of the vagus; but the exact path differs in different 

 animals. Thus in man (and in the rabbit) they reach the upper 

 part of the oesophagus by the recurrent laryngeal nerves and the 

 lower part through the oesophageal plexuses of the vagus (Fig. 70). 

 In the dog they descend to the oesophagus by the pharyngeal 

 branches of the vagus ; in the horse, the arrangement is still 

 different. Section of the trunk of the vagus renders difficult the 

 passage of food along the oesophagus, and stimulation of the 

 peripheral stump causes oesophageal 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 cesophagus 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 

 oesophageal 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 the 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 



