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GEORGE W. CORNER 



clearly from its neighbors. When we do find such a specimen of 

 the structm-al unit, it is entered by one artery (fig. 5, A. A.), 

 but has in addition many capillary anastomoses about its periph- 

 ery with the capillaries of the neighboring lobules. There is usu- 

 ally a chief venule (fig. 5, V.V.) which may or may not run along 

 with the artery. In addition, there are often one or two other 

 small veins connecting with the capillary net. 



Fig. 5 Diagrams of two units of the adult pancreas, drawn with the camera 

 lucida from thick sections of a specimen in which the blood-vessels have been in- 

 jected. AA, arterioles supplying units; VV, venules draining units; Is, dilated 

 capillaries of an island of Langenhans. X 20. 



Fig. .6 Cleared injection of adult pancreas, one unit dissected out, showing 

 ducts. U, unit-duct; S, straight ducts; P, pre-acinar ducts. X 40. 



Dogiel twenty years ago ('93) studied the ducts of the pan- 

 creas in sections of Cajal silver specimens, and described four 

 orders, as follows: (1) Large excretory ducts; (2) tubules of the 

 second order; (3) tubules of the third order, or ''Schaltstiicke;" 

 (4) very fine tubules of the fourth order, which often divide 

 again and finally enter the acini. 



