THE TONGUE 



339 



epithelial coat. The surface of the larger of these papillae is not smooth, 

 but is covered with small secondary papillae. 



The dorsal surface of the tongue presents a sharp structural differ- 

 ence between its anterior and posterior portions. The papillae are 

 limited to the anterior portion, which includes about two-thirds of 

 the entire surface; this is known as the papillary area. The posterior 



FIG. 319. ONE LATERAL HALF OF A CORONAL SECTION OF A DOG'S TONGUE. 



The dorsal surface presents numerous large filiform papillae, a, lingual papilla; ; 

 6, corium; c, the fibromuscular substance of the tongue. Hematein and eosin. 

 Photo. X 6. 



one-third lacks papillae, and is of lymphoid character, hence known as 

 the lymphoid area (lingual tonsil). These two areas represent the 

 originally separate anlages from which the definitive tongue develops: 

 the anterior unpaired tuberculum impar, and the posterior paired radix 

 lingua. The line of fusion is indicated in the fetus and infant by a 

 shallow V-shaped groove, the sulcus terminalis. This subsequently 

 disappears, and the boundary then remains marked by the position of the 

 circum vail ate papilla?. The papillary area constitutes the tongue proper. 

 EPITHELIUM. The epithelium of the tongue is of the stratified 



