256 THE DIGESTIVE ORGANS. 



glands may be regarded as made up of numerous smaller glands. 

 The ducts divide and redivide, as above described, with this exception, 

 that the secreting compartments are not joined to the intralobular 

 ducts, with striated epithelium, by means of narrow intermediate 

 ducts, as these divisions of the duct system are lacking in these 

 glands (Maziarski). The general arrangement of the secreting 

 compartments in a small portion of a sublingual gland is shown in 

 Fig- ! 99- The size of the tubules and alveolar enlargements 

 varies. In the tubules and alveoli there are two varieties of cells: 

 cells which form mucus and cells which have a serous secretion. 

 The cells which form mucus, appear clear in preparations treated 

 after the ordinary methods used in the laboratories. In fresh 



Fig. 199. Model of a small portion of a sublingual gland of man ; X I 4- The 

 demilunes of Heidenhain are more deeply shaded (Maziarski, " Anatomische Hefte," 

 1901). 



preparations teased in serum or in 2 ^ to 5 ^ sodium chlorid solu- 

 tion (Langley), or when fixed and stained after special methods, it 

 may be seen that the secretion is first formed in the form of large 

 granules, consisting of a substance known as mucigen, which 

 breaks down to form the mucus, much as described for mucous or 

 goblet cells (see page 87). In preparations the cells of which are 

 stored with mucigen the nuclei are situated at the periphery of the 

 tubules and alveoli, near the basement membranes. The cells with 

 serous secretion are situated in close apposition to the basement 

 membrane; they resemble in structure serous cells, and are found 

 either singly or in groups of crescentic shape. These groups are 

 known as the crescents of Gianuzzi or the demilunes of HeidenJiain. 

 The margins of the individual cells composing the crescents are 



