184 HISTOLOGY. 



also enters the tongue. Some of the muscle fibers are oblique but many 

 of the bundles cross at right angles. In the connective tissue between 

 them, medullated nerves are abundant. Some of these are sensory nerves 

 to the mucosa but many are the lingual branches of the hypoglossal nerve 

 which supply all the tongue muscles except the inferior longitudinal; that 

 one is supplied by fibers from the chorda tympani. Sensory spindles 

 have been found in the lingual muscles. 



The posterior part of the tongue is occupied by the lingual tonsil, 

 this term being a collective designation for a considerable number of 

 rounded masses of lymphoid tissue. Each of these, is from i to 4 mm. in 

 diameter, and is situated in the tunica propria so that it causes a low, 

 macroscopic elevation of the epithelium. In the center of the elevation 

 there is a punctate depression, or pit, lined with stratified epithelium. 

 Around it the lymphoid tissue is partly separable into nodules with germi- 

 native centers (Fig. 205). The entire lymphoid structure is bounded by 

 a sheath of connective tissue. Numerous lymphocytes enter the epithelium, 

 and pass between its cells to the free surface where they escape into the 

 saliva. The temporary disintegration of the epithelium, due to this cause, 

 is shown in Fig. 206. In all these details the lingual tonsil is essentially 

 like the palatine tonsils. 



MOUTH AND PHARYNX. 



The lining of the mouth, like the covering of the tongue, consists of 

 epithelium, tunica propria, and submucosa. At the lips toward the line 

 of transition from skin to mucous membrane, hairs disappear from the 

 skin. The epithelium becomes abruptly thicker but more transparent as 

 it crosses the line. Its outer cells are still cornified, but they are not so flat 

 and compactly placed as in the skin. The deeper cells appear vesicular. 

 Within the mouth, except on the tongue, cornified cells are absent. Gran- 

 ules of the refractive horny substance, keratohyalin, are said to occur in 

 the outer cells, even in the oesophagus. The outer surface of the epithelium 

 is smooth, but its under surface is indented by many connective tissue 

 papillae, which are particularly long and slender in the lips (Fig. 207) and 

 gums. Cilia occur on the epithelium in the highest part of the nasal 

 pharynx, and in the fetus over the oral part also, and even in the oesoph- 

 agus. They persist only in the nasal pharynx. 



The tunica propria, as is generally the case in the digestive tract, has 

 few elastic fibers. Some of its tissue is reticular and in this, lymphoid 

 accumulations are frequent; they may extend into the submucosa. On the 

 oral surface of the soft palate there is a layer of elastic tissue between the 

 propria and submucosa. A similar layer is found in the oesophageal end 



