THE MOUTH 



321 



with the underlying parts, but in (he hard palate and the gums this 

 union is very firm. 



Lymphoid tissue occurs in considerable abundance in the oral mu- 

 cous membrane. Areas 

 of diffuse lymphoid 

 tissue are of frequent 

 occurrence and small 

 lymph nodules are oc- 

 casionally found. The 

 lymphatic vessels form 

 a plexus in the tunica 

 propria, which empties 

 into larger vessels in 

 the submucosa. 



Secreting glands 

 occur in considerable 

 abundance in all por- 

 tions of the buccal 

 mucous membrane ex- 

 cept that covering the 

 gums. The glands are 

 of the tubulo-acinar 

 type and produce 

 either a pure mucous 

 secretion or, in the 

 case of the larger ones, 

 a mixed mucous and 

 serous secretion. The 

 ducts of the glands are 

 lined by cplumnar 

 cells which, near the 

 mouth of the duct, of- 

 fer a gradual transi- 

 tion to the stratified squamous epithelium of the mucosa. The glandular 

 epithelial cells of the secreting portions become swollen and clear after a 

 period of rest, but are shrunken and present a faint cytoplasmic reticu- 

 lum after aciiviiy. The different glands of the same region, and even 

 different cells in the same gland, often exhibit various stages of secretory 

 activity. The fundus of the secreting glands frequently extends into the 



loose connective tissue of the submucosa. At the margin of the lips and 

 21 



FIG. 301. FROM A SECTION THROUGH THE LIP OP 

 AN INFANT. 



a, cutaneous surface; b, epithelium of the oral mu- 

 cosa; c, layer of striated muscle; d, layer of mucous 

 glands. Hematein and eosin. Photo. X 10 



