306 SALIVAEY GLANDS AND PANCREAS 



ment membrane which, in the larger ducts, is invested with a fibro- 

 elasfcic coat containing a few longitudinal smooth muscle fibres. 



The ducts divide and subdivide in an arborescent manner, the 

 larger branches lying in the connective tissue which invests the 

 lobules into which the gland is subdivided, while the smaller 

 branches are found within the lobule. The duct system is thus 

 divisible into interlobular and intralobular ducts ; the latter in- 

 clude the " salivary " and intercalary ducts. 



In the smaller glands of the mouth the number of subdivisions 

 of the duct system is relatively small, but in the larger salivary 

 glands the small ducts are innumerable. Thus, in the submaxil- 

 lary gland, Flint * found that the interlobular duct system 

 formed 1,500 terminal branches, each of which entered a lobule 

 and was further subdivided into intralobular and intercalary ducts 

 before terminating in the secreting acini. The larger glands may 

 therefore be said to bear to the smaller ones represented in Fig. 

 247, a relation which is comparable with that of a full-grown tree 

 to the youngest sapling. 



The smaller interlobular ducts are lined by columnar epithe- 

 lium whose cells contain two zones, one on either side of the cen- 

 trally situated nucleus. The distal zone 

 or free extremity of the cell is finely 

 granular, the proximal zone or base pre- 

 sents a characteristic striated appearance 

 which is apparently due to a fibrillar 

 structure of the cytoplasm in this portion 

 of the cell. The epithelium is easily de- 

 tached from its basement membrane by 

 the artificial contraction of the tissues 

 during fixation and hardening. 



The lumen of the ducts is of consider- 



FIG. 249. INTERCALARY DUCTS 



diameter and contains the reticulated 



AND ACINI OF THE HUMAN 



SUBMAXILLARY GLAND, COR- or granular particles of the secretion. 



duct; The *"&* d ^ S ^ ^ Connective 



G, intercalary duct ; JJ, acini. tissue se P ta whlch mvest the 



Highly magnified. (After groups of acini. Each of these groups is 

 derived from the ramifications of the 



terminal branch of an interlobular duct which enters the lobule 



to divide into numerous intralobular ducts, and secondarily, 



through a short intermediate or intercalary portion, into the 



* Am. J. of Anat., 1902. 



