MOUTH CAVITY. 167 



Organs. Into the trench numerous serous glands (v. Ebner's) 

 open (Fig. 122). 



At the side of the tongue of some animals (mainly the 

 rabbit) there is found another kind of papilla, the papilla 

 foliata. There is in the rabbit a white area about 1 cm. long, 

 situated on each side of the posterior part of the tongue. It is 

 made up of many papillae foliate somewhat resembling the 

 circumvallate papillae, separated from one another by trenches 

 or furrows. They are covered with stratified epithelium, and 

 on their adjacent sides are many taste bulbs (see under Organs 

 of Taste- ). ' 



The submucosa of the tongue is firm at the tip and along 

 its dorsal surface, but looser elsewhere. 



The muscles of the tongue are cross-striated. Their arrange- 

 ment will be found in works on gross anatomy. In the frog 

 the muscle fibres are frequently seen to branch. Between the 

 muscle bundles there are glands, fat, and intramuscular con- 

 nective tissue. The lymphoid tissue of the tongue is spoken 

 of under " Lingual tonsils." 



The blood-vessels are spread out in a capillary network 

 under the epithelium, which is especially well developed in the 

 papillae. The lymphatics have a similar course. The nerves 

 end in part freely between the epithelial cells, and partly in 

 various terminal end organs (Krause's end bulbs, Meissner's 

 taste corpuscles. and taste buds). 



4. The Tonsils. 



The adenoid tissue is well developed around the borders 

 of the mouth cavity, forming an organ which Waldeyer has 

 called the lymphatic pharyngeal ring. This tissue may be 

 divided into three main masses, that which is in the tongue 

 (lingual tonsils), that associated with the palate (palatine 

 tonsils), and that situated in the pharynx (pharyngeal tonsils). 



The lingual tonsils (folliculi linguales) are situated in that 

 part of the tongue between the circumvallate papillae and the 

 epiglottis. They are round masses of adenoid tissue lying in 

 the upper part of the tunica propria, easily visible to the naked 



