174 MICROSCOPIC A ^ ATOMY OF THE ORGANS. 



circumvallate papillae of the tongue are serous glands. The 

 pure mucous glands are usually small and scattered throughout 

 the mouth cavity. The submaxillary and sublingual belong to 

 the mixed glands. 



In order to study the cell arrangement in both serous and 

 mucous glands, we shall consider that of a typical mixed gland, 

 human submaxillary, in which both are present. A diagram 

 of such a gland is given in Fig. 129. Here one can see an 

 intermediate part of the tube entering in one place serous 

 tubules ; in another place it enters a mucous tubule, which 

 becomes composed at the end of serous cells. To the right of 

 the diagram is an intermediate duct entering a mucous tubule 

 which ends blindly. At the end of this there is a cap-like 

 mass of cells resembling serous cells. In section they have the 

 form of a half-moon, and are known as the demilunes of 

 Gianuzzi. The significance of these cells is doubtful. Ac- 

 cording to R. Heidenhain, they are young gland cells which 

 take the place of mucous cells which have disintegrated. No 

 evidence of mitotic or amitotic division has ever been observed 

 in these cells. Other authors regard them as entirely separate 

 secreting cells, which have nothing to do with the mucous cells; 

 while some think they are merely mucous cells which have 

 discharged their secretion. There are sometimes to be observed 

 in these cells the so-called secretory canals or capillaries, which 

 are a continuation of the lumen of the tubule between neigh- 

 boring cells. They are found often in serous tubules, and are 

 sometimes much branched. They possess no wall of their own, 

 and are demonstrated most easily by Golgi's method, in which 

 the whole lumen is filled with the black precipitate. It is 

 highly probable that the demilunes of Gianuzzi have the power 

 of secreting an albuminous fluid ; and if this is the case, it 

 is necessary to consider all those mucous glands which contain 

 these cells as mixed glands (R. Krause). 



The salivary glands are richly supplied with blood-vessels. 

 The larger vessels run in the connective tissue between the 

 lobules. Here they break up into fine branches, enter the 

 lobules, and surround the tubules with a thick capillary net- 



