502 



SPECIAL PHYSIOLOGY. 



masticated, and softened by the saliva, is placed between the tongue 

 and the hard palate, and is then pressed backwards, by a movement of 

 the tongue, beneath the slightly sloping soft palate, which is rendered 

 tense by the circumflex muscles. The anterior pillars of the fauces 

 are separated, to receive the mass, whilst the posterior pillars and the 

 uvula, by being elevated and approximated in the manner just de- 

 scribed, shut off the upper part of the pharynx and the posterior nasal 

 openings. The tongue, becoming shorter and thicker, its posterior part 

 is rendered convex, and, by means of the mylo-hyoid muscles, which 

 form the muscular floor of the mouth, and also by the digastricus, stylo- 

 hyoids, and thyro-hyoids, is then forced upwards and backwards, and 

 following the mass of food, propels it, through the fauces, into the 

 middle portion of the pharynx ; thus is completed the first stage in the 

 act of deglutition. 



The second stage of deglutition is performed through, and by, the 

 pharynx. This is a musculo-membranous sac, or bag, about 4J inches 

 in length, and wider above than below, which is suspended from the 

 base of the skull, in front of the vertebral column, and behind the 

 cavities of the nose, mouth, and larynx, with all of which it communi- 

 cates. It is through the larynx, that the air passes to and from the 

 lungs. Qn a level with the lower border of the larynx, the pharynx 

 becomes continuous with the oesophagus, or gullet. The pharynx, Fig. 

 87, has seven openings leading into it. At its upper part, in front, 

 are the two posterior nares, w, or nasal openings ; at each side, are the 



Fig. 87. 



Fig. 87. Back view of the pharynx and part of the oesophagus, suspended from the base of the skull, and 

 laid open behind, n, openings of the nnsal cavities, called the posterior DHres. separated by a median sep- 

 tum, p, soft palate, with the uvula depending from it, in the centre. Below this, the arches of the fauces, 

 hounded by Its posterior pillars, beneath this arch, is seen the back of the tongue, e. the epiglottis, or 

 valve which protects the superior aperture of the larynx. I, the back of the Hrynx, seen in the opened 

 part of the oesophagus, o, the oesophagus. /, the trachea, or windpipe. 



apertures of the Eustachian tubes, which lead to the tympanic cavities 

 of the ears ; these four openings are above the level of the soft palate. 

 Below the soft palate, p, the pharynx opens, by the isthmus of the 



