THE MECHANICS OF DIGESTION 



1005 



ously, has had sufficient time to escape into the stomach. This inter- 

 ference invariably gives rise to painful sensations and regurgitation 

 of the food. 



It should also be noted that the afferent impulses which determine 

 the activity of the center of deglutition, cause a stoppage of the respir- 

 atory movements. This is important, because an inspiratory motion 

 occurring during deglutition, might draw the food into the respiratory 

 passage, whereas an expiration occurring at this time, might force it 

 into the nasal cavity. The fact that this inhibition of respiration is 

 effected with the help of the glossopharyngeal nerve, may be proved 

 by stimulating the fauces and neighboring regions of the pharynx, 

 either mechanically or electrically. We have previously seen that 

 an analagous reaction may be produced by the excitation of the 

 mucous membrane lining the 

 nasal (trigeminus) and laryngeal 

 cavities (sup. laryngeal nerve). 

 Thus, it cannot surprise us to find 

 that the introduction of a 

 stomach-tube gives rise to an 

 almost immediate inhibition of 

 respiration which persists even 

 after a severe cyanosis has been 

 established. Repeated attempts 

 at swallowing, however, will tem- 

 porarily remove the inhibition 

 and allow the subject to replenish 

 the oxygen content of his blood. 

 A close reflex relationship also 

 exists between the center of deg- 

 lutition and the cardiac center, 

 as is evinced by the fact that the 

 act of swallowing increases the 

 rate of the heart. 



FIG. 511. DIAGRAMMATIC REPRESENTATION 



OF THE STOMACH. 



C, Cardiac end; F, fundus; P, pylorus; 

 D, duodenum; CS, cardiac sphincter; SA, 

 sphincter antri pylori; PS, pyloric sphinc- 

 ter; V, valvulae conniventes. 



B. THE MOVEMENTS OF THE STOMACH 



The Movements of the Fundus and Pylorus. The muscular 

 coat of the stomach consists essentially of an outer longitudinal and an 

 inner circular layer. To these are added in certain areas of this organ 

 an inner layer of obliquely placed muscle strands which serve to 

 strengthen its wall along its anterior and posterior surfaces below the 

 cardia. The layer of circular strands is the heaviest of all and is of great- 

 est functional importance. At the pyloric and esophageal poles of the 

 stomach it suddenly increases in thickness, forming here the so-called 

 pyloric and cardiac sphincters. A third band of circular fibers invests 

 the stomach at the junction between its fundic and pyloric portions, 

 i.e., about 7 to 10 cm. above the pylorus. It is known as the sphincter 



