352 HANDBOOK OF PHYSIOLOGY. 



developed layer of longitudinal, uristriated muscle, called the muscularis 

 mucosce. The mucous membrane is composed of a closely felted mesh- 

 work of fine connective tissue, which, toward the surface, is elevated into 

 rudimentary papillae. It is covered with a stratified epithelium, of 

 which the most superficial layers are squamous. The epithelium is ar- 

 ranged upon a basement membrane. 



In newly-born children the mucous membrane exhibits, in many 

 parts, the structure of lymphoid tissue (Klein). 



Blood- and lymph-vessels, and nerves, are distributed in the walls of 

 the oesophagus. Between the outer and inner layers of the muscular 

 coat, nerve-ganglia of Auerbach are also found (fig. 254). 



DEGLUTITION. 



When properly masticated, the food is transmitted in successive por- 

 tions to the stomach by the act of deglutition or swallowing. The fol- 

 lowing account of deglutition is based upon the researches of Kronecker 

 and Meltzer, whose experiments seem to disprove the earlier theory of 

 Magendie: 



The mouth is closed, and the food is rolled after thorough mixing 

 with the saliva 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 

 oesophagus to the cardiac orifice of the stomach. Coincidently with 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 

 and thus closing the larynx. The interval of time between the com- 

 mencement of the act of deglutition and the arrival of the food at the 

 cardiac orifice of the stomach is not more than 0.1 second. Usually the 

 food remains at the cardiac orifice without entering the stomach until 

 the first pare of the act of swallowing is reinforced by the subsequent 

 contraction of the constrictors of the pharynx and the passage of a peri- 

 staltic wave down the oesophagus. This wave, reaching the cardiac ori- 

 fice about 6 seconds after the commencement of the act of deglutition, 

 forces the food into the stomach, the sphincter having previously re- 

 laxed. In some cases, however, the food is not stopped at the cardiac 

 orifice, but is sent through the relaxed sphincter by the original force of 

 the mylo-hyoid contraction. 



In man the oesophagus contracts in three separate segments the 

 first segment lying in the neck and being about 6 centimetres long, the 



