STRUCTURE OF THE TONGUE. r>83 



apertures leading into recesses of the mucous membrane. The 

 under surface, free only in part, gives attachment to the mucous Lower 

 membrane and to the different lingual muscles connected with the surface - 

 hyoid bone and the jaw. In front of the muscles the mucous 

 membrane forms a fold in the middle line, termed the frcenum 

 linguae.; and on each side an irregular ridge plica fimbriata (better 

 seen in infants), runs forwards and inwards about midway between 

 the fraenum and the margin of the tongue towards the tip. 



Each border of the tongue is joined opposite the lateral groove Borders, 

 above mentioned by the fold of mucous membrane descending from 

 the soft palate, and known as the anterior pillar of the fauces. 

 Behind this fold, the root of the tongue is attached on each side to 

 the wall of the pharynx ; but in front the margin of the body is free. 

 The free border i,3 thick and rounded in its hinder part, where it is 

 marked by vertical ridges and furrows, and becomes gradually 

 thinner towards the tip. 



PAPILLAE. On the dorsuni of the tongue are the following kinds Kinds of 

 of papillae ; the conical and filiform, the fungiform, and the 

 circumvallate. A hand lens may conveniently be used in the 

 examination of them. 



The conical and filiform papilla are the numerous small projec- conical 

 tions which cover the anterior two-thirds of the dorsuni of the 

 tongue. They taper from the base towards the free extremity, 

 where they are provided with smaller secondary papillae ; and 

 many of them, especially towards the sides of the organ, have their 

 epithelial covering produced into long hair-like processes, whence 

 the name filiform is given to them. Towards their limit behind 

 they are arranged in lines parallel to the lateral grooves, and on the 

 sides they form vertical rows. 



The fungiform papillce are less numerous but larger than the fungiform ; 

 preceding set, amongst which they are scattered, especially at the 

 tip and sides of the tongue. They are wider at the free end than 

 at the part fixed to the tongue, and project beyond the conical 

 papilke. Their surface is covered with small simple papillae. 



The circuntrallate papilla; are much larger than the foregoing, cireumval- 

 and are placed at the junction of the middle and posterior thirds 

 of the tongue. Their number varies from seven to twelve. One, 

 larger than the rest, is situate immediately in front of the foramen 

 ca'cum, and the others are disposed in two rows (one on each side) 

 parallel to the lateral groove, so as to form a figure like a widely- 

 spread letter V. Each papilla is attached by a constricted stem, 

 which is surrounded by a groove; its wider end or base projects 

 beyond the surface of the tongue, and is covered with small 

 simple papillae. Around the groove the mucous membrane forms 

 a slightly .prominent fold, which is also beset with secondary 

 papillae. 



STRUCTURE. The tongue consists of two symmetrical halves Parts^ found 

 separated by a fibrous layer in the median plane. Each half is 

 made up of muscular fibres with interspersed fat ; and entering it are 



