1128 



THE DIGESTIVE SYSTEM. 



The philtrura 



Anterior gland of 

 ** tongue 



Layer of muscle cut 



to show the gland 



Plica fimbriata 



central part (1 to 2-5 mm. wide), slightly tapering towards its base, and flattened 

 on its crown, which projects a little above the general surface of the tongue. This 

 is surrounded by a deep, narrow, circular trench or fossa, the outer wall of which 

 is known as the vallum. The vallum appears in the form of an encircling collar 

 very slightly raised above the adjacent surface (Fig. 891). 



As in the case of the other forms, the vallate papillae are made up of a central 

 mass of corium, studded with numerous microscopic papillae on the crowns, but not 

 on the sides, and covered over, as are the surfaces of the fossa and vallum, by 

 stratified squamous epithelium. Into the fossae open the ducts of some small 

 serous glands (Fig. 891 A). 



On the sides of the vallate papillae, as well as upon the opposed surface of 



the vallum, are found, in consider- 

 able numbers, the structures known 

 as taste-buds, the special end-organs 

 of the nerves of taste. 



Just anterior to the glosso- 

 palatine arch, on the margin, are \ 

 usually seen about five or six dis- ; 

 tinct vertical folds, forming the 

 folia linguae, which are studded with 

 taste-buds. They correspond to 

 the papillae foliatae on the side of 

 the tongue in certain animals 

 (rabbit, hare, etc.), in which they 

 form an important part of the 

 organ of taste. 



The apex and the margin of 

 the tongue in front of the attach- 

 Frenuiumiinguaj men t of the glosso-palatine arch 



Duct of the submax- 

 illary gland 

 Openings of ducts of 

 the submaxillary 

 gland 

 Sublingual gland 



Plica sublingualis, 

 with openings of 

 ducts of sublingual 

 gland 



the teeth when the tongue is at 

 rest. 



On the superior half or more of the 

 margin and apex, papillae are present as 

 on the dorsum ; but on the inferior part 

 they are absent, and the surface is covered 

 by smooth mucous membrane. 



FIG. 892. OPEN MOUTH WITH TONGUE RAISED, AND THE 

 SUBLINGUAL AND ANTERIOR LINGUAL GLANDS EXPOSED. 



The sublingual gland of the left side has been laid bare by the 

 removal of the mucous membrane ; to expose the anterior 

 gland of the right side a thin layer of muscle, in addition 

 to the mucous membrane, has been removed. A branch 

 of the lingual nerve is seen running on the medial aspect 

 of the gland. The vena profunda linguae is faintly in 

 dicated on this side also. 



The inferior surface of the 

 tongue, which is exposed by turn- 

 ing the apex of the organ upwards 

 is limited in extent (Fig. 892) 

 and is free from visible papillae 

 the surface being covered by a 

 smooth mucous membrane. Kun 

 ning along its middle, except 

 near the tip, is a depression, iron 



which a fold of mucous membrane, the frenulum linguae, passes down to the flooi 

 of the mouth, and on towards the posterior aspect of the mandible. At eacl 

 side of the frenulum, and a short distance from it, the large profunda lingua 

 vein is distinctly seen through the mucous membrane. Further out still ar< 

 situated two indistinct, fringed folds of mucous membrane, the plicae fimbriatse 

 which converge somewhat as they are followed forward towards the tip, near whicl 

 they are lost. 



From the inferior surface of the tongue the mucous membrane passes acros 

 the floor of the mouth to the medial surface of the gum, with the mucous coverin; 

 of which it becomes continuous. 



The plicae nmbriatffl correspond pretty closely to the course of the deep lingual arteries as the 



