i86 



NORMAL HISTOLOGY. 



lished, probably there is no interchangeability between the two varieties of 

 epithelium. Independence of function is generally conceded, and, further, 

 that the islets are to be regarded collectively as an organ of internal secretion, 

 producing a substance, which, either directly or by way of the lymphatics, 

 enters the blood and serves an important purpose in regulating carbohydrate 

 metabolism. Their distribution throughout the pancreas is by no means 

 uniform, since they may be almost double in number towards the tail. 



The pancreatic duct, or duct of Wirsung, empties into the second 

 part of the duodenum, usually by an orifice common to it and the common 

 bile-duct. This relation is explained by the fact, that the beginning of the 

 later pancreatic duct is derived from an outgrowth of the wall of the primary 



FIG. 232. Section of injected pancreas, showing intralobular capillary network; also vascular 

 convolutions of islands of Langerhans. X 50. 



liver-diverticulum that becomes the bile-duct, both excretory canals being 

 th,us closely connected from the first. The walls of the main duct and its 

 larger branches contain numerous small tubular mucous glands and bundles 

 of unstriped muscle. At its lower end, the circular bundles are condensed 

 and augmented into a sphincter-like band that encircles its duodenal orifice. 

 The blood-vessels supplying the pancreas are distributed to the 

 glandular tissue in accordance with the usual plan for such structures. The 

 positions of the interalveolar cell-groups, however, are indicated in minutely 

 injected organs by corresponding areas in which the capillary network is 

 exceptionally dense (Fig. 232). The lymphatics are represented by 

 definite channels accompanying the interlobular blood-vessels to which the 

 intralobular lymph-spaces are tributary. The nerves are composed chiefly 

 of nonmedullated sympathetic fibres distributed to the walls of the blood- 

 vessels and of the larger ducts, some passing to the alveoli. Ganglion-cells, 

 scattered or grouped, lie along the interlobular trunks. 



