314 



FOOD AND DIGESTION 



The mouth is closed, and the food after thorough mixing with the saliva 

 is rolled into a bolus on the dorsum of the tongue. The tip of the tongue is 

 pressed upward and forward against the hard palate, thus shutting off the 

 anterior part of the mouth cavity. The mylo-hyoid muscles then suddenly 

 contract, the bolus of food is put under great pressure and shot backward and 

 downward through the pharynx and into the esophagus and, if the food be 

 fluid enough, even to the cardiac orifice of the stomach. Coincidently with 



FIG. 252. Transverse Section of the Human Esophagus, a, Fibrous covering; b, longi- 

 tudinal muscular fibers; c, transverse muscular fibers; d, areolar or submucous coat; e, muscularis 

 mucosae; /, mucous membrane, with part of a lymphoid nodule; g, stratified epithelial lining; h, 

 mucous gland; , gland duct; m', striated muscle fibers. (V. Horsley.) 



the contraction of the mylo-hyoid muscles, the hyoglossi are thrown into 

 action, drawing the tongue backward and downward, not only increasing 

 the pressure upon the food, but forcing the epiglottis over the glottis, closing 

 the larynx. 



It has been shown by the Roentgen-ray method that the character of the 

 food determines somewhat its passage through the esophagus. The dry 

 and semisolid foods are seized by the musculation of the esophagus and passed 

 down that organ by a peristaltic wave. The longitudinal muscles contract, 

 tending to enlarge the diameter of the esophagus in advance of the food, while 

 contractions of the circular muscles produce pressure on the bolus just 

 behind, thus forcing it along to the cardia. This wave reaching the 

 cardiac orifice about six seconds after the commencement of the act of 



