PHARYNX. 



953 



related to the internal carotid artery, which 

 vessel will be applied to its outer side and be- 

 hind it, so that when an opening is required in 

 the tonsil, the point of the lancet should be 

 directed inwards towards the cavity of the 

 mouth. The tonsils and soft palate are well 

 supplied with blood by the palatine and ton- 

 sillitic branches from the facial, by the ascend- 

 ing pharyngeal and internal maxillary arteries. 

 A considerable plexus of veins is formed round 

 the tonsil, which terminates in the pharyngeal 

 venous plexus. Besides the nervous twigs de- 

 rived from the palatine branches of Meckel's 

 ganglion, the soft palate also receives filaments 

 from a plexus formed around the tonsils by the 

 tonsil litic branches of the glosso-pharyngeal, 

 which has been called the circulus tonsillaris. 

 For the description of the tongue, the remaining 

 boundary of the cavity of the mouth, see 

 TONGUE. 



Course of the mucous membrane. The mu- 

 cous membrane of the mouth is continuous 

 with that of the pharynx and larynx. Com- 

 mencing with the gums anteriorly, it passes 

 upon the exterior surfaces of the upper and 

 lower maxillary bones, and from thence is re- 

 flected on the cheeks laterally and upon the 

 inner surface of the lips anteriorly, forming a 

 small fold in the median line, called thefrcenum, 

 to each ; it invests the free borders of the lips 

 and becomes continuous with the skin at a well 

 defined line of demarcation. When the jaws 

 and teeth are closed, the cheeks and lips are 

 naturally in apposition with them ; but if sepa- 

 rated by distending the cheeks, the mucous 

 membrane we have been tracing will be seen 

 to line an anterior or second buccal cavity form- 

 ing a kind of antechamber to the interior of the 

 mouth. Proceeding from the gurns posteriorly 

 the membrane descends upon the interior of 

 the lower jaw to be reflected upwards to the 

 under surface of the tongue, and forms for it 

 anteriorly and in the median line a prominent 

 fold, the frcenum linguae ; this occasionally is 

 prolonged forwards to the apex of the tongue, 

 interfering with its movements in the act of 

 sucking : a slight division of the frcenum under 

 these circumstances is all that is required. From 

 the under surface of the tongue the mucous 

 membrane invests that organ and is continued 

 from its base to the epiglottis, and after forming 

 three folds, called glosso-epiglottic, is reflected 

 over its free edge to be continuous with the 

 laryngeal membrane. From the gums of the 

 upper jaw posteriorly it invests the hard and 

 soft palate and passes round the posterior free 

 border of the latter, after enclosing the uvula, 

 to cover its nasal surface. From the cheeks 

 laterally it is to be traced over the anterior 

 pillars of the fauces, the internal surface of the 

 tonsils dipping into its mucous crypts, and 

 lastly forming the folds of the posterior pillars 

 is continuous with the mucous membrane of 

 the pharynx. Throughout the cavity of the 

 mouth it is invested with epithelial scales, and 

 its submucous areolar tissue is remarkably in- 

 creased in thickness and density when forming 

 the gums and palate. 



Function. The pharynx, mouth, and palate 

 are most obviously associated in the process of 

 deglutition, in which we may trace three suc- 

 cessive stages : in the first, the food after being 

 reduced to a softened pulp by mastication and 

 admixture with the saliva is conveyed to the 

 back part of the mouth by the movements of 

 the tongue against the hard palate; this is a 

 purely voluntary act and can be arrested at the 

 will of the individual : the food carried past 

 the anterior arch of the fauces, the second act 

 of deglutition immediately succeeds ; this in- 

 volves the consentient action of numerous mus- 

 cles and is a most complicated process. If the 

 movements of the velum palati and the poste- 

 rior pillars of the fauces are examined during 

 an effort to swallow, the former is perceived to 

 become somewhat more arched towards the 

 cavity of the mouth and to be rendered tense, 

 but it appears to maintain nearly its naturally 

 oblique direction. It has been supposed that 

 the velum is raised during deglutition, in order 

 to prevent the food from passing to the nose, 

 but this opinion is now generally considered 

 erroneous. Muller says, " Most writers incor- 

 rectly state that during deglutition the food is 

 prevented from entering the posterior nares by 

 the soft palate being raised, a movement which, 

 if performed, could not in any case completely 

 cut off the pharynx from the posterior nares." 

 With the stretching of the velum the posterior 

 pillars or palato-pharyngei muscles will be 

 seen to approach each other, particularly above, 

 so as to reduce the isthmus faucium to a narrow 

 triangular slit, broadest below. If the food is 

 now pressed backwards by the tongue, it will 

 be urged through this dilatable chink in a 

 direction downwards and backwards,occasioned 

 partly by the oblique resisting surface of the 

 velum, and partly by the wider aperture left 

 between the posterior pillars inferiorly, perhaps 

 also by their greater disposition to yield in 

 that direction to the pressure of the food as it 

 passes between them ; meanwhile the pharynx 

 (and the larynx with it) has been drawn up- 

 wards, and at the same time widened by the 

 action of the stylo-pharyngei muscles, to receive 

 the morsel, which in passing into it presses the 

 epiglottis down upon the superior aperture of the 

 larynx, and gliding over it is then immediately 

 carried on to the oesophagus by the action of 

 the constrictor muscles. The epiglottis in 

 being shut down upon the opening of the 

 larynx protects the respiratory tube, but it is 

 not absolutely essential for that purpose ; ex- 

 periments have been performed on animals 

 where the epiglottis has been removed, and it 

 has been destroyed by disease in the human 

 subject without any material difference evi- 

 denced in deglutition, the action of the laryngeal 

 muscles closing the aperture of the larynx. 

 This second act of deglutition may be performed 

 at will though only the saliva is swallowed, 

 but the effort soon becomes fatiguing. When 

 the food, however, has reached beyond a cer- 

 tain limit in the mouth, no effort on our part 

 can prevent deglutition from taking place. (For 

 the influence of the nerves upon this function 



