738 PHYSIOLOGY. 



The circumvallate papilla, the largest of the varieties and about 

 a dozen in number, form a V-like row, defining the papillary layer 

 at the posterior third of the tongue. They have the form of an 

 inverted cone surrounded by a ringlike wall-elevation. 



The fungiform are next in size, and more numerous than the 

 circumvallate. They are small, red eminences scattered over the sur- 

 face of the tongue, but are especially numerous at and near the tip. 

 They are rounded at the free extremity and narrower at the point of 

 attachment to the tongue. 



The filiform papilla?, smaller and more numerous than the 

 others, are crowded in the spaces between the others, but are ar- 

 ranged in rows diverging from the median line of the tongue. 



Nerves. The tongue receives three nerves: one of motion, the 

 liypoglossal, which animates the muscles; and two other sensory 

 branches the lingual branch of the glosso-pharyngeal and the lingual 

 branch of the trigeminus. The former of the latter two branches 

 spreads in the mucous membrane at the base and edges of the tongue; 

 the latter is distributed to the mucous membrane of the anterior two- 

 thirds of the tongue. The branches of the glosso-pharyngeal are 

 especially concerned in sensations of bitterness, while the branches of 

 the trigeminus are affected principally by sweet and acid tastes. 



Section of the hypoglossal upon both sides causes paralysis of the 

 tongue without injuring its tactile or gustatory sensibilities. Section 

 of the lingual branch of the trigeminus causes only loss of fine tactile 

 sensibility and gustatory sensibility of the anterior two-thirds of 

 the tongue. 



Section of the glosso-pharyngeal causes loss of tactile and gusta- 

 tory sensibility in the mucous membrane at the base of the tongue. 

 Such an animal can swallow bitter and nauseous substances, like 

 colocynth, with impunity. 



The gustatory action of the lingual branch of the trigeminus 

 comes from the chorda tympani. The latter is a small nerve which 

 begins in the facial and traverses the middle ear to join the lingual 

 branch at the level of the pterygoid muscles. 



The chorda tympani nerve passes from the tongue to the nerve- 

 centers through the lingual nerve, the facial, and finally through the 

 intermediate nerve of Wrisberg. 



Taste-organs. The terminal branches of the glosso-pharyngeal 

 nerve end in the taste-bulbs. The taste-bulbs are oval bodies imbedded 

 in the epithelial layer. Each taste-bulb is formed of two kinds of 

 elongated epithelial cells, and their whole outline is barrel-shaped. 



