376 MOVEMENTS OF (ESOPHAGUS. [BOOK n. 



It will be remembered that the muscular bundles of the oeso- 

 phagus are composed of striated fibres in the upper part, and of plain 

 unstriated fibre-cells in the lower part, the transition occupying a 

 different level in different animals. Nevertheless, as far as the 

 peristaltic movement is concerned, the two kinds of fibres behave 

 in the same way .except that the peristaltic wave if we may so 

 call it travels more rapidly in the striated region. 



These peristaltic movements of the oesophagus may, like those 

 of the intestine, be seen after removal of the organ from the body \ 

 and indeed may continue to appear upon stimulation, for an 

 unusual length of time. They may therefore be carried out by 

 the muscular elements, with or without the help of the nervous 

 elements embedded in them, apart from any action of the central 

 nervous system. Nevertheless, in the living body, the movements 

 of the oesophagus seem to be in a special way dependent on the 

 central nervous system; the contractions are not started and 

 carried out by the walls of the tube alone and so transmitted from 

 section to section in the walls of the tube itself ; but afferent im- 

 pulses started in the pharynx and passing to the medulla oblongata, 

 give rise to reflex efferent impulses which descend along 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 con- 

 traction, 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, viz. 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 oesophageal movements 

 can easily be excited by centripetal stimulation of the superior 

 laryngeal. The centre lies in the medulla oblongata, being a part 

 of the general 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 

 oesophageal plexuses of the vagus (Fig. 84). Section of the trunk 

 of the vagus ' renders difficult the passage of food along the oeso- 

 phagus, 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 oesophagus with the stomach the circular 



