MASTICATION AND DEGLUTITION. 



495 



the stomach, the Saliva may afford important aid in the digestive process. 

 (See 668 and 863.) When the reduction of the food in the mouth has 

 been sufficiently accomplished, it is carried into the oesophagus by the action 

 of Deglutition. The share which the nervous system has in this action has 

 been already stated ( 382) ; and it here only remains to define more pre 

 cisely the different movements which are concerned in it. These were lirst 

 described in detail by Magendie; but his account requires some modification, 

 through the more recent observations of DzondL* Theirs? stage in the pro- 

 cess is the carrying back of the food, until it has passed the anterior palatine 

 arch; this, which is effected by the approximation of the tongue and the 



[Fig. 200. 



.30 



29 



28 



A view of the Muscles of the Tongue, Palate, Larynx and Pharynx as well as the position of the 

 upper portion of the CEsophagus, as shown by a vertical section of the head; 1, 1. the vertical section of 

 the head; 2, points to the spinal canal; 3, section of the hard palate; 4. inferior spongy bone ; 5. middle 

 spongy bone ; 6, orifice of the right nostril ; 7, section of the inferior maxilla; 8, section of the oshyoides; 

 9, sectionofthe epiglottis: 10. section of the cricoid cartilage ; 11. the trachea, covered by its lining mem- 

 brane; 12. section of sternum; 13, inside of the upper portion of the thorax; 14, genio-hyo-glossus muscle; 

 15, its origin ; 10, 17, the fan-like expansion of the fibres of this muscle; 18, superficialis lingua; muscle; 

 19, verticales linguae muscle; 20, genio-hyoideus muscle: 21. mylo-hyoideus muscle; 22, anterior belly 

 ofdigastricus; 23, section of platysma myoides; 24, levator menii : 25. orbicularis oris; 26. orifice of Eus- 

 tachian tube ; 27, levator palati ; 28, internal pterygoid ; 29, section of velum pendulum palati, and azy- 

 gos uvulas muscle; 30, stylo-pharyngeus ; 31, constrictor pharyngis superior; 32. constrictor pharyngis 

 medius; 33, insertion stylo-pharyngeus; 34, constrictor pharyngis inferior ; 35, 36, 37, muscular coat of 

 esophagus; 38, thyreo-arytenoid muscle and ligaments, and above is the ventricle of Galen :jS9, section 

 of arytenoid cartilage ; 40, border of sterno-hyoideus.] 



palate, is a purely voluntary movement. In the second stage, the tongue is 

 carried still further backwards, and the larynx is drawn forwards under its 

 root, so that the epiglottis is depressed down over the rima glottidis. The 

 muscles of the anterior palatine arch contract after the morsel has passed it, 

 and assist its passage backwards; these, with the tongue, cut off completely 

 the communication between the fauces and the mouth. At the same time, the 

 muscles of the posterior palatine arch contract in such a manner, as to cause 



* Miiller's Physiology, p. 501. 



