1064 ORGANS OF SPECIAL SENSE 



tinguished. The filiform papillae are the smallest and most numerous, and are fili- 

 form or conical in shape and thickly cover the ventral two-thirds of the dorsum and 

 also the lateral margins and apex. They are arranged in faintly marked lines which 

 are parallel posteriorly with the terminal sulcus, but become more transverse towards 

 the tip. They are best developed dorsally in the middle line, and those which are 

 largest and longest are known as the conical papillas. The fungiform papillae are 

 scattered irregularly among the preceding over the dorsum, lateral margins, and apex 

 of the tongue, being most numerous in the two latter situations. The epithelium 

 covering them is thinner than in the filiform papilla?, and they are, therefore, redder in 

 colour. Each consists of a comparatively narrow base supporting a broader, rounded, 

 free extremity. Many on the margins are flattened or lens shaped, and are called 

 lenticular papillas. The vallate (circumvallate) papillae, seven to twelve in num- 

 ber, are the largest. They are arranged in a V-shaped line ventral to the terminal 

 sulcus and parallel with it. Each presents an attached base slightly narrower than 

 the broad, flattened, free top, and is situated in a circular depressed fossa surrounded 

 by a slight ridge, so that the top of the papilla and the ridge project but slightly above 

 the surrounding surface. In the fossa one or more serous glands open. The foliate 

 papillae are represented by six or seven vertical folds of mucous membrane separated 

 by grooves. They are situated upon the lateral margin of the tongue just ventral 



FIG. 761. TRANSVERSE SECTION THROUGH THE LEFT HALF OF THE TONGUE. 



(Magnified.) 



(From a preparation by Mr. J. Pollard, Middlesex Hospital Museum.) 



Traiisversus linguae 



LongitudinaliB 

 superior 



Septum 



Longitudmalis in- 

 ferior (mixed 

 with extrinsic 

 fibres) 



Verticalis linguae 



to the glosso-palatine arch, and are more or less rudimentary in man, compared with 

 their development in some of the lower mammals. 



The gustatory organ is formed by microscopic special end-organs of taste, the 

 caliculi gustatoria or taste-buds, which, besides being found upon the epiglottis 

 and velum palatinum (soft palate), are located on the vallate, fungiform, lenticular, 

 and foliate papilla, but are absent from the filiform and conical. 



Beneath the mucous membrane of the posterior third of the tongue abundant 

 lymphoid tissue is collected to form nodular masses of variable size, the lingual 

 follicles, which are grouped together under the name of the lingual tonsil. They 

 extend from the terminal sulcus to the epiglottis, and laterally as far as the palatine 

 tonsils. The lingual glands which lie beneath the mucous membrane of the lingual 

 tonsil are especially abundant near the foramen ca-cum and around the vallate and 

 foliate papilla?. A special group forms on each side of the frenulum, and just' 

 medial to the tip of the tongue, an oval mass, the anterior lingual glands (glands 

 of Nuhn or Blandin) , which are partially covered by muscular fibres. 



Muscles of the tongue. A layer of fibrous connective tissue, the lingual sep- 

 tum, separates the halves of the tongue, extending in the median plane from the apex 

 to the base, where it is attached to the hyoid bone. The muscles of the tongue are 

 classified as extrinsic and intrinsic. The extrinsic muscles are the hyo-slossus, 

 genio-glossus, stylo-glossus, and glosso-palatinus (palato-glossus) , and part of the. 



