OF MASTICATION AND DEGLUTITION. 223 



its arch, and whose use is not clearly understood, is 

 extended by muscles of its own, and closes those 

 openings.* 



The tongue protects the glottis, for the larynx at the 

 moment of deglutition is drawn upwards and forwards, 

 and in a manner concealed under the retracted root of 

 the tongue and applied to the latter in such a way, that 

 the glottis, being also constricted and protected by the 

 epiglottis, is most securely defended from the entrance 

 of foreign substances. (B) 



348. Deglutition is facilitated by the abundance of 

 mucus which lubricates these parts, and which is af- 

 forded not only by the tongue (237), but by the nu- 

 merous sinuses f of the tonsils and cryptae of the 

 pharynx. 



349. The oesophagus, through which the food must 

 pass previously to entering the stomach, is a fleshy 

 canal, narrow and strong, mobile, dilatable, very sen- 

 sible, and consisting of coats resembling, except in 

 thickness, the coats of the other parts of the alimentary 

 canal.;}: 



The external coat is muscular, and possesses longi- 

 tudinal and transverse fibres. 



The middle is tendinous, lax, more and more cellular 

 towards each of its surfaces, by which means it is con- 

 nected with the two other coats. 



The interior is lined, like all the alimentary tube, 



* Santorini, Tab. Post hum. IV. — vi. fig. 2. — and vn. 

 B. S. Albinus, Tab. Muscular, xn. fig. 11, 27, 28. 

 f B. S. Albinus, Aunotat. Acad. L. in. tab. in. fig. 1, n. 

 X MaUh. Van. Gcuns, Verhandelingen van de Maaisdutppye te Haarlem. 

 T. XI. p. 9 sq. 

 Jan. Blculand, Obscrv. de structura esophagi. LB. 1785. 4to. 



