280 The Ducts of the Human Submaxillary Gland 



branch, although they not infrequently end in ampullae without giving 

 rise to a single vessel of a similar nature, especially in the mucous parts 

 of the gland. 



At the ends of the intercalary ducts are the ampulla of the alveoli 

 in which they terminate. These are surrounded by the secreting 

 epithelium of the alveolus and represent moulds of the spaces into 

 which the secretion is poured from the cells before it passes into the 

 intercalary ducts. They have constricted necks marking the termi- 

 nation of the ducts and the end of this portion of the secreting sys- 

 tem. Beyond the constriction their greatest diameter may be twice 

 as large as the duct from which they spring. In corrosions they 

 (Fig. 3) appear like ovoid knob-like endings to the intercalary ducts 

 occurring in groups or clusters. As a rule they are slightly longer than 

 they are wide, occasional ampullas, however, are much longer than 

 others, showing that they must have been derived from longer alveoli. 

 In Fig- 3 the two apical ampnllse represent alveoli of this nature. Ap- 

 parently the number of these structures arising from an intercalary 

 duct varies between three and six, four perhaps representing the aver- 

 age number. This means, of course, that four alveoli, on an average, 

 empty into each of the termini of the intercalary ducts. Wliether they 

 represent primary reservoirs for the storage of the products of glandu- 

 lar metabolism before they are emptied into the ducts it is as yet im- 

 possible to say. 



In the course of development of the submaxillary gland the growing 

 ducts, as we have already seen, are accompanied by blood-vessels which 

 maintain thronghout life this close and intimate association. Since 

 blood-vessels follow in general certain laws of ramification, each trunk 

 of the same size in an organ tending to give off an equal number of 

 branches, it is not unreasonable to assume that the ducts may perhaps 

 obey some similar law. Blood-vessels, of course, are not in stable 

 equilibrium but are continually subjected to progressive and regressive 

 changes which depend upon certain well-known laws.' The caliber of 

 the vessel, for example, depends on the velocity of the current within 

 it and this, in turn, depends partly on the nature and number of its 

 branches. So far as we know the cross-section of the ducts is not the 

 resultant of the action of any mechanical factors like those influencing 

 the progressive and regressive changes in vessels, although it is by no 

 means certain that some such mechanical control is not exerted. But 

 even while it is true that there is a general tendency for ducts of the 



''Thoma's Uutersnclmne^en iiber die Histogenese und Histomecbanik des Gefass- 

 systems. Stuttgart, 1893. 



