THE TONGUE. 145 



The posterior or lymphoid area, the part of the dorsum behind the 

 circumvallate papillae, presents a striking contrast to the anterior two thirds 

 of the mucous membrane. The surface is thrown into uncertain rounded 

 elevations, which, while smooth and devoid of papillae, impart to this portion 

 of the tongue ah uneven and mammillated appearance that is further accen- 

 tuated by numerous minute pits. The latter lead into small crypts, each 

 lined by stratified epithelium continued from the surface and surrounded by 

 a zone of lymphoid tissue. The latter contains a number of lymph-nodules, 

 with germ-centres, blended together by the intervening diffuse lymphoid 

 tissue and lodged in the tunica propria. These spherical masses, fatfotticuli 

 linguales, resemble in miniature the lymphoid organs found on the side-walls 

 of the oro-pharynx and, hence, are often termed collectively the lingual tonsil, 



The glands of the tongue include both mucous and serous varieties, 

 which are distributed in three groups: (i) the serous glands, (2) the mucous 

 glands and (3) the anterior sero-mucous glands. The serous glands are 

 small and occur in the vicinity of the circumvallate and foliate papillae, 



Lymph-nodes 



Glands 



FIG. 185 Section from posterior third of child's tongue, showing lymphoid tissue constituting a part of 



the lingual tonsil. X 30. 



occupying the deeper part of the tunica propria, with some alveoli between 

 the subjacent muscle-bundles. Their ducts lead through the mucosa and 

 open preferably at the bottom of the furrows along which the taste-buds are 

 lodged. They belong to the tubo-alveolar group, with the tubular type of 

 the ultimate compartments pronounced. The gland-cells are somewhat pyram- 

 idal, rest upon a basement membrane of great delicacy, and secrete a thin, 

 watery, albuminous fluid. The mucous glands are found just in advance of 

 the more median circumvallate papillae, along the margins of the tongue, and 

 scattered through the lymphoid area, especially towards the root. They are 

 tubo-alveolar in type and among the examples of pure mucous glands. 

 Their viscid, mucin-containing secretion is produced by the cylindrical 

 gland-cells and carried off by ducts, which are lined with columnar epithe- 

 lium and open on the free surface or, not infrequently, into the lymphoid 

 crypts. The anterior lingual glands, or glands of Nuhn, form two elon- 

 gated groups, 15-20 mm. long and 7-9 mm. wide, which lie near the tip of 

 the tongue, on either side of the mid-line. Both serous cells and mucous 

 alveoli occur, hence they belong to the mixed mucous and tubo-alveolar type 

 and possess demilunes. They open on the under surface of the tongue. 



The blood-vessels of the tongue include, in addition to the branches 

 of the lingual artery that break up into capillary networks supplying the 

 muscles, a vascular meshwork within the mucous membrane from which 

 twigs ascend to the papillae. Each of the latter contains a tuft of elongated 



