44 



THE EPITHELIAL TISSUES 



branches alone possess the secretory cells and the other portions 

 form the excretory duct system. The mucous glands of the mouth 

 cavity, the prostate, and the kidney are examples of such tubular 

 glands. 



Fig. 20 



Fio. 21 



Fig. 20. — Simple alveolar gland (frog skin). 



Fig. 21. — Simple branched alveolar gland (sebaceous). 



Compound glands are invested with loosely arranged connective 

 tissue extending l)et\veen the excretory ducts and secretory end- 

 pieces. The large masses thus separated by connective tissue are 

 known as lobes and the smaller subdivisions are called lobules. 



Fig. 22 



Fig. 23 



Fig. 24 



Fig. 22. — Compound tubular gland. 



Fig. 23. — Compound tubular-alveolar gland (submaxillary). 



Fig. 24. — Compound alveolar gland (lung). 



The main excretory- ducts accompanied by blood and lymph vessels, 

 and ner\'es are carried in the connective tissue between the lobules. 

 Immediately surrounding the basement membrane of the gland cells 

 of the secreting end-pieces is a capillary network and also a plexus 

 of nerve fibers. 



