410 STRUCTURE OF A SALIVARY GLAND. [BOOK n. 



subdivides into a number of smaller ducts. Each of the ultimate 

 divisions of the duct at last ends in a ' secreting ' portion, which 

 is lined by a 'secreting' epithelium different in character from 

 the epithelium lining the ducts. Such a terminal secreting 

 portion is called an alveolus. Sometimes a duct terminates in 

 a single alveolus, which then appears as a swollen or somewhat 

 flask-shaped termination of the duct distinguished from the 

 duct by the size and character of its cells and by the narrow- 

 ness of its lumen ; but more commonly a duct ends in several 

 alveoli, which then appear as a number of short curved somewhat 

 swollen tubes, branching off from the end of the duct. All the 

 ducts and the alveoli in which they end are bound up by connec- 

 tive tissue, carrying blood vessels, nerves and lymphatics, into a 

 compact, rounded but somewhat lobulated mass, the gland proper. 

 Each alveolus, or each group of alveoli, and the small duct of 

 which it forms the blind end is surrounded and separated from its 

 neighbours by a certain amount of connective tissue. A number 

 of alveoli with the ducts leading to them are bound together into 

 a lobule by a rather larger amount of connective tissue. Groups of 

 these smaller lobules are bound together by connective tissue and 

 enveloped by a more distinct coat of that tissue, and thus form 

 larger or primary lobules; and these larger lobules are bound up to 

 form the gland itself by a quantity of connective tissue, which also 

 forms a wrapping or sheath for the whole gland. Hence a thin 

 section taken through the gland is seen, when examined under a 

 low power, to be divided by septa of connective tissue (continuous 

 with the sheath of the gland, and carrying blood vessels, &c.), into 

 irregular areas, which are generally angular from compression. 

 These areas are sections of the primary lobules, and each may 

 be seen to be similarly but less distinctly subdivided into similar 

 smaller areas, the smaller lobules. Each of these smaller lobules 

 will in turn be seen to be for the most part made up of rounded 

 bodies varying somewhat in size and shape but on the whole very 

 much alike, bound together by a small amount of connective 

 tissue ; these are the alveoli which, being disposed in various direc- 

 tions and being frequently more or less curved, are cut in various 

 planes by the section. Where the section cuts the alveolus trans- 

 versely the outline of the alveolus is circular, where obliquely the 

 outline is more elliptical; a section moreover may pass through 

 the mere tip or side of the alveolus and so miss the lumen 

 altogether; and indeed many varied appearances may be presented. 

 Among these alveoli are seen other bodies of a somewhat different 

 aspect, circular, elliptical or cylindrical in outline, or hour-glass- 

 shaped, or even irregular in form. These are the small tubular ducts 

 cut in various planes. Sections of the larger ducts of various size 

 may also be seen in the septa between the lobules. Even with 

 quite a low power it is easy to distinguish between the alveoli or 

 secreting elements and the ducts, and when we come to examine 



