THE TONGUE 



391 



Thyroid 



Foliate 

 'papilla 



the ventral surface of the tip. It varies considerably in thickness. On the dorsum 

 it is very thick and dense ; underneath this part there is a dense fibrous cord, which 

 extends medially a distance of five or six inches forwafd~frbm the vallate papillse. 

 On the sides and ventral surface of the tongue the membrane is much thinner and 

 smooth, and can more readily be dissected off the muscular tissue.^ From the 

 lower surface of the free part of the tongue a fold of the mucous membrane passes 

 to the floor of the mouth, forming the frenum linguae. Posteriorly a fold passes 

 on each side from the edge of the dor- 

 sum to join the soft palate, forming the 

 anterior pillars of the latter. A thick 

 central glosso-epiglottic fold (Plica 

 glossoepiglottica) passes from the root 

 to the base of the epiglottis; this en- 

 closes the hyoepiglottic muscle. The 

 mucous membrane presents numerous 

 papillae, which are of four kinds — fili- 

 form, fungiform, vallate, and foliate. 

 The filiform papillae (Papillse filiformes) 

 are fine, thread-like projections which 

 stud the dorsum and the sides of the 

 tip; they are absent on the root. On 

 the anterior part they are so small as 

 to be scarcely visible, but on the pos- 

 terior part they are much larger and 

 give the surface a distinct pile. The 

 f longif orm papillae (Papilla f ungif ormes) 

 are larger and easily seen; they are 

 rounded at the free end, which is sup- 

 ported by a neck. They occur princi- 

 pally on the lateral part of the tongue, 

 but are also found scattered over the 

 dorsum. The vallate papillae (Papillae 

 vallatse) are usually two or three in 

 number. The two constant ones are a 

 quarter of an inch or more (ca. 6 to 7 

 mm.) in diameter, and are found on 

 the posterior part of the dorsum, one 

 on each side of the median plane, about 

 an inch (ca. 3 cm.) apart. The third, 

 when present, is behind these, is cen- 

 trally situated, and is always smaller. 

 Rarely a fourth may be found. They 

 are rounded, broader at their exposed 

 than at their attached surfaces, and are 

 sunk in a depression which is bounded 

 by an annular wall. Their free surface 



is tuberculate, i. e., bears small, round secondary papillae The foliate papilte 

 (PapilliB foliate) are situated just in front of the anterior pillars of the soft palate, 

 where they form a rounded eminence about an inch (ca. 2 to 3 cm.) m iengtn, 

 marked by transverse fissures. The last three varieties are covered with micro- 

 scopic secondary papillse and are furnished with taste-buds. The mucous mem- 

 brane of the root of the tongue presents numerous folds and rounded elevations. 

 1 The mucous membrane is thick and closely adherent where food naturally comes in contact 

 with the tongue. 



Vallate 

 papilla 



Trachea 



Crico-arytinoid- 



ens doTsalis 



muscle 



A rytenoideus 



muscle 

 Arytenoid carti- 

 lages 



Vocal cord 



Aditus laryngis 

 Epiglottis 



Tonsil 



Radix linguoe 



Anterior pillar of 

 soft palate (cut) 



Dorsum linguce 



Fig. 331.- 



Apex lingua 



Tongue, Larynx, and Part of Trachea of 

 Horse; Dorsal View. 



