226 THE DIGESTIVE SYSTEM 



The Tongue consists of a muscular mass, partially covered 

 by mucous membrane. Its anterior part lies almost horizontally 

 in the floor of the mouth, while its posterior part lies almost 

 vertically in the anterior wall of the oral part of the pharynx 

 (Fig. 86). The junction of the anterior two-thirds with the 

 posterior third of the tongue is marked in the median plane 

 by a small depression, termed the foramen ccccum, which 

 possesses considerable morphological interest (p. 411). Immedi- 

 ately in front of the foramen caecum, the vallate papillae are 

 arranged in a V-shaped manner on the dorsum of the tongue. 



Collections of lymphoid tissue, termed the lingual tonsil, are 

 situated under the mucous membrane of the pharyngeal portion 

 of the tongue. They are of interest because they are very 

 constantly enlarged in cases of status lymphaticus. 



The sensory nerve-supply of the tongue is derived from the 

 lingual and the glosso-pharyngeal nerves (pp. 75 and 92), while 

 the muscles of the tongue are supplied by the hypoglossal 

 nerve (p. 107). 



The lymph vessels from the tip of the tongue join the 

 submental glands (p. 225); those from the borders and sub- 

 stance of the tongue pass to the submaxillary lymph glands 

 (p. 221) and thence to the upper anterior group of the deep 

 cervical glands ; those from the base of the tongue pass 

 directly to the latter group. 



The Isthmus Faucium forms the communication between 

 the mouth and the oral part of the pharynx. It is bounded, 

 above, by the soft palate : below, by the tongue : and, on 

 each side, by the glosso-palatine arch (anterior pillar of the 

 fauces), which extends from the lateral part of the lower 

 surface of the soft palate to the side of the tongue. 



The Oral Part of the Pharynx lies behind the isthmus 

 faucium. Above, it communicates freely with the naso- 

 pharynx, but this communication is completely shut off when 

 the soft palate is elevated. 



A fold of mucous membrane, termed the pharyngo-palatine 

 arch (posterior pillar of the fauces), extends downwards on the 



