326 DIGESTION 



for four or five seconds, and this cessation is distinguished from 

 that produced by any other afferent nerve by the circumstance 

 that it occurs not in expiration exclusively or in inspiration ex- 

 clusively, but with the respiratory muscles in the precise degree of 

 contraction in which they happened to be at the moment of stimu- 

 lation. The efferent nerves of the reflex act of deglutition are the 

 hypoglossal to the tongue and the thyro-hyoid and other muscles 

 concerned in raising the larynx; the glosso-pharyngeal, vagus, 

 facial and fifth to the muscles of the palate, fauces, and pharynx; 

 the fifth to the mylo-hyoid; and the vagus to the larynx and 

 oesophagus. Section of the vagus interferes with the passage of 

 food along the oesophagus; stimulation of its peripheral end causes 

 cesophageal movements. 



Movements of the Stomach. The whole of the stomach does 

 not take part equally in the movements associated with digestion. 

 We may divide the organ, both anatomically and functionally, into 

 two portions a pyloric portion, or antrum pylori, comprising about 

 a fifth of the stomach, and a larger cardiac portion, or fundus* 

 At the junction of the antrum and the fundus the circular muscular 

 coat is slightly thickened into a ring called the ' transverse band/ 

 or ' sphincter of the antrum.' In the living stomach the region 

 of the transverse band is usually contracted so strongly and con- 

 tinuously that a distinct groove is seen to separate the tubular 

 antrum from the bag-like cardiac end. The suggestion of a massive 

 constricting ring of muscle is belied by an examination of the dead 

 viscus. The transverse band is really little more than a physio- 

 logical sphincter. The empty stomach is contracted and at rest. 

 A few minutes after food is taken contractions begin in the antrum, 

 and run on in constricting undulations (in the cat at the rate of 

 six in the minute) towards the pyloric sphincter. Each wave takes 

 about twenty seconds (in the cat) to pass from the middle of the 

 stomach to the pylorus. Feeble at first, they become stronger and 

 stronger as digestion proceeds, and gradually come to involve the 

 portion of the fundus next the sphincter of the antrum, but their 

 direction is always towards the pylorus, never, in normal diges- 

 tion, away from it. The food is thus subjected to energetic churn- 

 ing movements in the pyloric end of the stomach, and worked up 

 thoroughly with the gastric juice. Kept in constant circulation, 

 it gradually becomes reduced to a semi-liquid mass, the chyme, 

 which is at intervals driven against the pylorus by strong and 

 regular peristaltic contractions of the lower end of the stomach, 



* Here ' fundus ' is used in the sense in which it is generally employed in 

 speaking of the stomach of the dog 01 cat as signifying the wnole of the organ 

 with the exception of the antrum pyiori. By the fundus of the human stomach 

 most writers mean only the cul-'Je-sac at the cardiac end; the portion inter- 

 vening between it and the aucrum pylori is often termei the body of the 

 ttomach. 



