430 HEAD AND NECK 



is free ; the upper border of the base forms the lower boundary 

 of the isthmus faucium. 



Mucous Membrane. The lingual mucous membrane is 

 a part of the general mucous lining of the buccal cavity. 

 The dorsum of the tongue, when the mouth is closed and 

 the organ is at rest, is strongly arched antero-posteriorly, 

 and, for the most part, is moulded into the vaulted roof of 

 the mouth. The tongue consists of two developmentally 

 distinct parts, termed oral and pharyngeal. These are 

 marked off from each other, even in the adult, by a V-shaped 

 groove called the sulcus terminalis. The apex of this sulcus 

 points posteriorly, and coincides with a median blind pit 

 which receives the name of the foramen ccecum. From this 

 the two limbs of the sulcus diverge antero-laterally, and they 

 reach the margins of the tongue at the attachments of the 

 glosso-palatine arches. 



The oral part of the tongue, by its upper or dorsal 

 surface, stands in relation to the hard palate, and to some 

 extent to the anterior part of the soft palate also. The 

 pharyngeal part of the tongue looks posteriorly, and forms 

 the anterior wall of the oral portion of the pharynx. In its 

 upper part it is related to the soft palate, whilst below it is 

 intimately related to the epiglottis. On the lateral wall of the 

 pharynx, immediately above this portion of the tongue, is 

 the tonsil. 



The mucous membrane which envelops the tongue 

 presents very different appearances in different localities. 

 That portion which is spread over the pharyngeal part of 

 the tongue, and is prolonged upwards over the surface of 

 the tonsil, is smooth and somewhat glossy and presents no 

 visible papillae. It is from this district that the glosso- 

 epiglottic fold takes origin, and every here and there the 

 surface is studded with low projections, which are produced 

 by lymph follicles placed subjacent to the mucous membrane. 

 Each of these small elevated areas, as a rule, presents in the 

 centre a minute pit, visible to the naked eye. 



Anterior to the foramen caecum and sulcus terminalis the 

 mucous membrane which covers the dorsum, sides, and tip 

 of the oral part of the tongue is beset with papillae of 

 different kinds. As these are individually visible to the naked 

 eye the mucous membrane presents a very characteristic 

 appearance. Further, a median groove or sulcus extends 



