186 MUCOUS MEMBKANES 



of epithelium, in which a distinct lumen soon appears, and which 

 grows into the surrounding mesoblast, carrying with it its embry- 

 onal tunica propria. 



The form of the glandular invaginations is subject to great 

 variation. They may be straight and simple, more or less branched 

 and compound, convoluted or coiled, or the tubules may terminate 

 in minute ampullary enlargements, the acini. The invaginations 

 may also be distinctly tubular and of approximately equal diameter 

 throughout, or they may form pouch-like saccules. According to 

 the form of the organ, it is thus possible to distinguish the following 



HISTOLOGIC TYPES OF SECRETING GLANDS: 



1. Simple. 



2. Convoluted. 

 I. Tubular <j 3. Branched. 



I 4. Compound. 

 I 5. Compound tubulo-acinar. 

 f 1. Simple. 

 II. Saccular 4 2. Branched. 



I 3. Compound. 

 III. Ductless secreting glands. 



Glands of the tubular and saccular types contain an actively 

 secreting portion or fundus and a duct. In the ductless glands 

 the latter is absent. The duct, though its epithelium may take 

 some part in the formation of the glandular secretion, primarily 

 serves to convey the secretion of the fundus to the free surface of 

 the mucous membrane. 



The epithelium of the duct, as a rule, more or less closely re- 

 sembles that of the mucous membrane upon whose surface it opens. 

 The epithelium of the fundus, on the other hand^usually differs 

 from that of the duct and varies according to the nature of its 

 secretion. In many of the glands the epithelium is typically 

 mucus secreting ; others produce a clearer, watery, and less viscid 

 serous secretion. Hence it is possible to distinguish the following 



PHYSIOLOGIC TYPES OF SECRETING GLANDS: 



I. Serous glands. 

 II. Mucous glands. 



III. Glands which are both mucous and serous (mixed glands). 



IV. Glands which are neither mucous nor serous. 



