378 MANUAL OF HISTOLOGY. 



Elsewhere the mucosa is looser, so that the mucous mem- 

 brane is readily thrown into folds. It is thickest wherever it 

 has intervening layers of- glands. In some places, especially 

 in the lips and soft palate, the submucosa is crossed by bun- 

 dles of striped muscular fibres, which are connected partly 

 with the submucosa, and partly with' the tunica propria. The 

 papilla of the mucous membrane are most developed at the 

 margin of the lip and its immediate vicinity, as well as on the 

 gums, attaining here a height of 0.5 mm., and often termina- 

 ting in a double point. In the reduplications of the mucous 

 membrane (the frsenum linguae, etc.), and partly in the region 

 of the hard palate, the papillae are very small, sometimes rudi- 

 mentary. The thickness of the epithelial layer is proportion- 

 ate to the height of the papillse. Beginning at the vermilion 

 border of the lips, and going backward, the epithelial cov- 

 ering becomes progressively thicker, and is thickest at the 

 posterior margin of the lip, decreasing rapidly on the pos- 

 terior surface. Upon the cheeks and on the anterior surface 

 of the hard palate the epithelium is of medium thickness ; 

 it is thinnest on the floor of the mouth and on the above- 

 mentioned reduplications. There are, however, deviations in 

 these proportions, especially in the hard palate, where the 

 papillse are in some cases absent. Moreover, the tunica pro- 

 pria sometimes assumes an almost tendinous character. Cer- 

 tain important aggregations of glands, the so-called mucous 

 glandules, are found lodged in the submucous connective tis- 

 sue of the mouth. These are the labial, buccal, palatal, and 

 molar glandules. They are found as white, sharply defined 

 knobs, visible to the naked eye upon the posterior surface of 

 the lips, as well as upon the cheeks, palate, and bottom of the 

 buccal cavity. In some cases they are aggregated into a few 

 large clusters, while in others they are more scattered and 

 smaller. The orifices of their ducts are best seen in the lining 

 membrane by everting the lips or cheek. They belong to the 

 acinous type, and have a short duct, generally somewhat 

 curved, relatively wide, but somewhat contracted at the ori- 

 fice. The greatest width of the tubes is at their place of seg- 

 mentation. On the branches themselves are smaller ramifica- 

 tions, which either terminate directly with globular or ellipsoid 

 alveoli, or previously divide into one or more twigs. It often 

 happens that a small group of acini, with a narrow common 



