118 



THE GLANDULAR TISSUE. 



The microscope lias been most industriously employed in 

 the examination of the minute structure of the glands, and 

 to it are we indebted for most of our knowledge on this 

 subject. 



The combination of the two elementary forms constitutes 

 compound glands, of which two varieties are noticed. 



1st. Those whose tubes ramify in an arborescent form. 



2d. Where they do not branch off, but preserve the same 

 diameter nearly throughout their whole course. 



The mammary, salivary and lachrymal glands, with the 

 pancreas and the liver, belong to the first division. This 

 division presents two groups. 



FIG. 17. 



1. The tubes branch 

 off with some de- 

 gree of regularity, 

 the first branches 

 sending off others, 

 and these at certain 

 intervals again divid- 

 ing, till at their ter- 

 minations, to the na- 

 ked eye they present 

 the form of acini lo- 

 bules, or granuli, 

 which, saysMuller, are "only aggregates of cells, seated in 

 clusters on the extremities of the most minute secreting 

 canals or tubes, which cells are only visible by the micro- 

 .scope." These minute tubes sometimes branch off into 

 delicate coeca, as seen in the lachrymal glands of the 

 turtle, or into the form of tufts of twigs in other animals. 

 In the second group, the tubes branch off irregularly 

 and do not terminate in cells, but in tufts or twigs. The 

 liver is given as an example, and though it contains acini, 

 they are nevertheless composed of these tufts or twigs. 



FIG. 17 represents a portion of the Mammary Gland, and arborescent 

 arrangement of its ducts. 66 cc dd ee Lactiferous ducts and orifices, g g 

 g g Milk cells. /// Excretory ducts from the cells to the larger lac- 

 tiferous ducts. 



