70 GLANDS,- MUCOUS AND SEROUS MEMBRANES. 



internal as well as external secretions. Thus, the glycogenic 

 and urea-forming functions of the liver and the relation of the 

 pancreas to glycosuria are instances of internal secretory action. 

 Morphology of secretory glands (Figs. 31-34) : The secret- 

 ing glands, according to their form, are divisible into two 

 classes: tubular and saccular ; each of these, again, may be 

 simple or compound. 



Simple tubular glands consist of single tubes lined with 

 epithelium, with one end closed and blind and the other 

 opening on the skin or mucous surface. The glands of 

 Lieberkiihn and some of the gastric and uterine glands are 

 typical examples ; the sweat-glands are single tubes, modified 

 in having the secreting portion much coiled. 



In compound tubular glands the tubular structure is still 

 present, but the tubes branch and divide, discharging into a 

 common duct. Some of the gastric and uterine glands 

 exhibit the simplest gradations into this type. The kidneys, 

 testicles, and liver are compound tubular glands. 



Simple saccular glands consist of a single rounded or 

 spherical cavity or glandular sac with a small outlet to the 

 surface. Some of the simplest sebaceous glands may be of 

 this type, but they scarcely occur otherwise in mammals. 



Compound saccular or racemose glands, as the salivary, 

 mucous, lachrymal, sebaceous, and mammary glands, consist 

 of numbers of saccules opening into common ducts, and these 

 again uniting in larger ducts, much like a bunch of grapes. 

 In compound glands the ultimate saccules or alveoli which 

 communicate with common ducts form well-marked groups, 

 so that a division of the gland into lobes and lobules is easily 

 recognizable. The lobular divisions of glands are usually 

 separated by distinct partitions of connective tissue, inter- 

 lobular^ septa. Well-marked divisions of the ducts are also 

 recognizable, corresponding to their degree of division and to 

 their situation and relation to the lobules. Within a lobule is 

 a small division of the ducts, the. intralobulur dud, into which 

 the ultimate alveoli of that lobule all empty. The short duct 

 by which each individual saccule or alveolus empties into the 

 intralobular duct is called an intermediate duct; the union of 

 the intermediate ducts forms the intralobular ducts. The 

 intralobular ducts unite to form the interlobular ducts, which 



