158 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



of a large size, and that the amount of mucin increases gradually, forcing the 

 nucleus and a small part of the unchanged protoplasm toward the base of the 

 cell. Eventually the mucin is extruded bodily into the lumen of the intestine, 

 leaving behind a partially empty cell with the nucleus and a small remnant of 

 protoplasm (see Fig. 67). The complete life-history of these cells is imper- 



FIG. 67. Formation of secretion of mucus in the goblet cells: A, cell containing mucin; B, escape of 

 the mucin ; C, after escape of the mucin (after Paneth). 



fectly known. According to Bizzozero 1 they are a distinct variety of cell and 

 are not genetically related to the ordinary granular epithelial cells by which 

 they are surrounded. According to others, any of the columnar epithelial cells 

 may become a goblet cell by the formation of mucin within its interior, and 

 after the mucin is extruded the cell regenerates its protoplasm and becomes 

 again an ordinary epithelial cell. However this may be, the interesting fact 

 from a physiological standpoint is that these goblet cells are genuine unicellular 

 mucous glands ; moreover, the deposition of the mucin in the form of definite 

 granules within the protoplasm gives histological proof that this material is 

 produced by a metabolism of the cell -substance itself. It will be found that 

 the mucin cells in the secreting tubules of the salivary glands exhibit similar 

 appearances. So far as is known, the goblet cells do not possess secretory 

 nerves. 



SALIVARY GLANDS. 



Anatomical Relations. The salivary glands in man are three in num- 

 ber on each side the parotid, the submaxillary, and the sublingual. The 

 parotid gland communicates with the mouth by a large duct (Stenson's duct) 

 which opens upon the inner surface of the cheek opposite the second molar 

 tooth of the upper jaw. The submaxillary gland lies below the lower jaw, 

 and its duct (Wharton's duct) opens into the mouth-cavity at the side of the 

 fraenum of the tongue. The sublingual gland lies in the floor of the mouth 

 to the side of the franum and opens into the mouth-cavity by a number (8 to 

 20) of small ducts, known as the ducts of Rivinus. One larger duct which 

 runs parallel with the duct of Wharton and opens separately into the mouth- 

 cavity is sometimes present in man. It is known as the duct of Bartholin 

 and occurs normally in the dog. In addition to these three pairs of large 

 glands a number of small glands belonging both to the albuminous and the 

 1 Archivfur mikroskopische Anatomie, 1893, vol. 42, p. 82. 



