THE ACT OF SWALLOWING. 279 



place in the mouth. The passage of the bolus through the palatine arches on 



^ p ^^-^ e ^^ c ^-^^ 



nerves an question for the striated muscles lies in the medulla oblongata Degluti- 

 rftSn'^LSS^ m rt Stat ? f unconsei usn ^s, as well as after destruction 

 -,,ti .r P h P H,, m and pons. Irritation of the ninth cranial nerve prevents the 



S. 



Me. 



Within the esophagus (Fig. 107), the stratified squamous epithelium 

 of which is kept slippery by the mucus from small mucous glands opening 

 at the edges of the folds of mucous membrane, the downward movement 

 takes place also involuntarily through a coordinated muscular act a 

 peristaltic movement of 

 the external (longitu- 

 dinal) and the internal 

 (circular) unstriated 

 muscle-fibers. 



In the upper part of 

 the esophagus, in which lie 

 striated muscle-fibers, peris- 

 talsis is much more rapid 

 than in the lower portion. 

 The movements of the 

 esophagus never originate 

 spontaneously, but they al- 

 ways follow on a previous 

 act of deglutition. Thus, 

 if a bolus be introduced 

 into the esophagus through 

 an external wound, it re- 

 mains where it was placed; 

 it is carried downward only 

 when movements of deglu- 

 tition are initiated above. 

 The peristalsis extends 

 throughout the e h t i r e 



length of the esophagus, even if this be ligated or a portion has been excised. 

 The peristalsis, likewise, continues downward in a dog, even after meat is with- 

 drawn from the esophagus, though it has been halfway down. 



Exceedingly large and exceedingly small masses of food are swallowed with 

 greater effort than those of medium size. Dogs are able to swallow a bolus 

 weighing 450 grams. Deglutition becomes difficult in consequence of great dilata- 

 tion of the thorax, as in Miiller's experiments ; likewise in consequence . of con- 

 traction of the thorax, as in Valsalva's investigations. 



The motor nerve of the esophagus is the pneumogastric after division of which 

 on both sides food remains in the esophagus, particularly its lower part. 



Goltz discovered the remarkable fact that the ganglionic plexuses situated in 

 the esophagus and the stomach of the frog acquire greatly increased irritability 

 when the brain and spinal cord or both pneumogastric nerves are destroyed. 

 Esophagus and stomach contract vigorously like a string of pearls, even after 

 slight irritation, while animals with an uninjured central nervous system swallow 

 fluid introduced simply by peristalsis. It should be borne in mind that human 

 beings with an enfeebled nervous system (hysteria) not rarely exhibit similar spas- 

 modic contraction of the esophagus (globus hystericus). Schiff observed spas- 

 modic contraction of the esophagus in dogs also after section of both pneumo- 

 gastric nerves. 



The heart -beats are accelerated with each act of swallowing, while the blood- 

 pressure falls, the need of respiration diminishes and some movements, such as 

 labor-pains and erection, are inhibited. All of these movements are brought about 

 through reflex influences. 



FIG. 107. Transverse Section through the Esophagus. E, epithe- 

 lium ; St, mucous membrane ; Se, mucous gland ; Me, circular 

 muscle-fibers ; Ml, longitudinal muscle-fibers ; G, capillaries ; 

 B, connective tissue; S, submucosa. 



