MOVEMENTS OF THE STOMACH. 321 



tion of the palate and fauces. It is interesting to note that it can only 

 be inaugurated in this way, and that stimulation applied to the mucous 

 surface of the oesophageal tube is without effect and produces no 

 contraction. 



There is an important interdependence between the functions of 

 respiration and deglutition. The small inspiratory movement depends 

 on intra-bulbar connections between the two centres. 1 More important, 

 however, is the inhibition of respiration which occurs during swallow- 

 ing. Without this inhibition, food particles might be drawn by the 

 ingoing current of air into the bronchi and lungs, and would there set 

 up inrlammation. This inhibition of respiration is a reflex act, and is 

 carried out by the intermediation of the glosso-pharyngeal nerve. As 

 has been already mentioned, in dealing with the respiratory movements, 2 

 excitation of the central end of the glosso-pharyngeal nerve at once 

 causes a cessation of respiration, in whatever phase it may happen to 

 be. This cessation lasts for five or six seconds, i.e. a sufficient length 

 of time for a whole series of acts of deglutition. Kespiration then 

 recommences, and the inhibition cannot be prolonged by continuing the 

 stimulation of the glosso-pharyngeal nerve. 



Movements of the Stomach. 



The movements of the stomach have a twofold purpose. In the first 

 place, they serve to churn up the ingesta with the gastric juice, and, in 

 the second place, to propel the semi-digested chyme onwards into the 

 duodenum and intestines. 



The muscular coat of the stomach consists of three layers — an outer 

 longitudinal layer, continuous with the longitudinal fibres of the oesophagus ; 

 a middle or circular ; and an inner incomplete layer of oblique fibres, passing 

 from the left of the cardiac orifice, and merging at the pyloric end in the 

 middle or circular coat. 



The pyloric part of the stomach is divided by a special thickening of the 

 circular fibres, the "transverse band" 3 or "sphincter antri pylorici," 4 into 

 two parts, the antrum, between the band and the pylorus, and the pre-antral 

 portion or middle region of the stomach. 



If the stomach be examined in a fasting animal, care being taken to 

 avoid stimulation by cooling or drying on exposure to the air, it will be 

 found to be in a state of rest in slight tonic contraction. Owing to this 

 contraction, the cavity of the stomach is small, the walls are fallen 

 together, and the mucous membrane, which cannot retract with the 

 muscular coat, is thrown into rugae. When food is taken, the walls of 

 the stomach relax in proportion to the distension of its cavity, each 

 act of swallowing being, moreover, accompanied by a special dilatation 

 of the cardiac orifice, carried out mainly by the radiating longitudinal 

 fibres in the outer muscular coat. Shortly after the taking of food 

 irregular contractions of the gastric wall begin, and these become more 

 active as digestion advances. According to Beaumont's observations on 

 Alexis St. Martin, 5 these movements are of such a character as to pro- 



1 Marckwald, loc. cit. 2 Vide p. 305. 



3 William Beaumont, "Experiments and Observations on the Gastric Juice and the 

 Physiology of Digestion," edited by William Combe, Edinburgh, 1838, p. 107. 



^ 4 Hofmeister and Schiitz, Arch. f. exper. Path. 11. PharmaloL, Leipzig, 1886, Bd. x\\ 

 • s - ~ - 5 Beaumont, «/». cit. 



VOL. II. — 2 1 



