230 



HISTOLOGY 



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FIG. 219. FLOOR OF THE PHARYNX OF A IO-MM. HU- 

 MAN EMBRYO. 



I-IV. Branchial arches; t 1 , anterior part of the tongue! 

 t*, second arch, joining the posterior part of the 

 tongue toward the median line. The thyreoid 

 gland is dotted. The epigk>ttis extends over the 

 fourth arch. (From McMurrich, after His.) 



DEVELOPMENT AND STRUCTURE OF THE TONGUE. 



The tongue consists of two parts, an anterior and a posterior, which 



differ in origin and adult structure. Separating the branchial clefts from 



one another there are columns 

 of tissue known as branchial 

 arches. They come together in 

 the median ventral line to form 

 the floor of the mouth (Fig. 

 219). In this figure the upper 

 jaw and roof of the pharynx 

 have been cut away; the bran- 

 chial clefts are seen as dark de- 

 pressions bounded laterally by 

 thin plates. The first branchial 

 arch (i) is between the oral 

 and auditory clefts. In the 

 median ventral line an eleva- 

 tion (tuberculum impar) arises 

 between this arch and the 

 second; it becomes continuous 



with a larger elevated portion of the mandibular arch to form the anterior 



part of the tongue (t 1 ). The second and third arches unite toward the 



median ventral line and there produce the 



posterior part of the tongue (t 2 ). Between 



the anterior and posterior parts is the opening 



of the thyreoglossal duct, later the foramen 



caecum. . The epiglottis is an elevated part 



of the third arch separated from the poste- 

 rior part of the tongue by a curved groove. 

 In the adult (Fig. 220) the dor sum of the 



anterior part of the tongue is roughened with 



elevations or papilla. These are chiefly the 



slender filiform papilla and conical papilla; 



but knob-like forms, the fungiform papilla, 



are scattered among them over the entire 



surface, and in life they can be easily distin- 

 guished owing to their red color. Near the 



junction of the anterior and posterior parts of 



the tongue there is a V-shaped row of larger 



papillae, generally six to twelve in number, 



called vallate papilla. Their name refers to the deep narrow depression 



which encircles them. Behind the apex of the V, which is directed 



i.f, 



L1 



FIG. 220. THE UPPER SURFACE OF 

 THE ADULT TONGUE. 



c., Conical papillae; ep., epiglottis; f., 

 foliate papillae; f. c., foramen 

 caecum; f.f., position of the fili- 

 form and fungiform papillae; 1., 

 lenticular papilla; 1. t., lingual 

 tonsil; p. t., palatine tonsil; v., 

 vallate papillas. 



