DEGLUTITION. 



.an 



58. The opening which occupies the back part of the mouth, 

 and which forms the communication between this cavity and the 

 pharynx, is called the isfhniux of the throat, isthmus faucium. 

 During mastication, it is closed by the veil of the palate, (velum 

 palati,) but when deglutition is about to take place, this species of 

 curtain is raised, and the alimentary ball is pushed into the pharynx. 



59. The pharynx, ( Fiy. 2 1 , ph.) 

 is a cavity, situate between the 

 base of the cranium, and the front 

 of the neck; above, it communi- 

 cates with the nasal fossa3 by the 

 posterior nares or nostrils, (an), as 

 well as with the mouth, and below 

 it presents two openings ; one, by 

 which it is continuous with the 

 oesophagus, the other, situated in 

 front and called glottis, by which 

 it communicates with the larynx 

 and windpipe. We may compare 

 it lo a cross-road where the route 

 followed by the air to get from the 

 nose to the lungs, crosses the route 

 followed by the food to get from 

 the mouth to the oesophagus. 



60. That deglutition may be 

 effected, the alimentary ball must 



pass beneath the posterior nostrils and over the glottis, without 

 entering it, and descend directly into the oesophagus. 



Explanation of Fig. 21. A vertical section of the head and neck, to show 

 how the windpipe or trachea opens into the swallow or pharynx, and how 

 this last cavity communicates with the mouth and nasal fossae or nostrils, 

 b. the mouth, /. the tongue, vp. arch of the palate, which separates the 

 mouth from the nasal fossae, n,n. nasal fossae, opening externally by the nos- 

 trils and communicating with the swallow by the posterior nares or hind 

 nostiils, (an.) i. isthmus of the fauces, am. tonsils. c. veil of the palate, 

 pn. the swallow or pharynx, cleft or divided like the mouth and nasal fossae, 

 ft. oesophagus, a tube which descends from the swallow to the stomach, la. 

 larynx, the superior opening- of which, called the glottis, (si.) is placed at the 

 anterior and inferior part of the swallow : we see upon this organ, a species 

 of little tongue or valve, called epiglottis, (ep.) t. trachea or windpipe, 

 wnich descends from the larynx into the lungs, cr. base of the skull, 

 gsm. sub-maxillary gland, gsl. sub-lingual gland, ct. thyroid gland. 



58. What is the isthmus of the throat ? 

 during mastication ? 



59. What is the pharynx? 



60. What is necessary to effectual deglutition ? 



G2 



Is this cavity opened or closed 



