330 



THE TONGUE. 



The papillse, besides being the parts chiefly concerned in the special 

 sense of taste, also possess, in a very acute degree, tactile sensibility ; 



and the filiform papillae, armed 

 Fig- -""^- with their denser epithelial 



covering, serve a mechanical 

 use, in the action of the tongue 

 upon the food, as is well illus- 

 trated by the more developed 

 form which these papillae 

 attain in many carnivorous 

 animals. The papillary sur- 

 face of the tongue is supplied 

 abundantly with nerves. In 

 the papillae fungiformes the 

 nerves are large and nu- 

 merous, and form a plexus 

 with brush-like branches ; but 

 they are still more abundant, 

 and of greater size, in the 

 papillae circumvallatfB, where 

 they are chiefly distributed in 

 the neighbourhood of the taste- 

 buds (fig. 227). 



Glands. — The mucous mem- 

 brane of the tongue is pro- 

 vided with numerous small 

 racemose glands called lingual 

 glands, collected principally 

 about the posterior part of its 

 upper surface, near the pa- 

 pillae vallatje and foramen 

 c^cum, into which last the 

 ducts of several open. These 

 glands have commonly been 

 supposed to secrete mucus, 

 but it has been recently as- 

 certained that some of them, 

 those, namely, which ojjen in 

 the trenches around the pa- 

 pilla vallate, and at other 

 parts where taste-buds occur, 

 yield a more watery secretion 

 (Elner). Other small glands are found also beneath the mucous mem- 

 brane of the borders of the tongue. There is, in particular, a group 

 on the under surface of the tongue on each side near the apex. They 

 are there aggregated into a small oblong mass, out of which several 

 ducts proceed and open in a line on the mucous membrane. 

 ' The mucous membrane of the tongue, at least its posterior part, is 

 largely composed of retiform or lymphoid tissue, which is collected at 

 numerous points into the denser nodular masses known as follicular 

 glands, or lymphoid follicles. The blood-vessels and lymphatics of this 

 part of the membrane are numerous and large, but the papilla on its sur- 

 face are comparatively small, and are completely concealed by the thick 



Fig. 231. — Two Filiform Papill.?;, one with 

 Epithelium, the other without. 35 Dia- 

 meters. (From Kolliker, after Todd and 

 Bowman). 



p, the substance of the papiUre divided at 

 their ujiper extremities into secondav} lapillre ; 

 a, artery, and v, vein, connected by capillary 

 loops ; e, epithelial covering, laminated be- 

 tween the papillaj, but extended into hair-like 

 processes, /, from the extremities of the 

 secondary papillte. 



