PANCREAS. 



231 



accessory duct is sometimes obliterated, but it may remain pervious and 

 be of clinical importance in case of obstruction of the main duct. It opens 

 about an inch above the papilla. (In the pig, which is often studied 

 embryologically, the dorsal ? pancreas enters the duodenum distal to the 

 papilla; its duct persists whereas that of the ventral pancreas is obliter- 

 ated.) 



As is true of most glands, the developing tubules of the pancreas are 

 at first solid, but in the pancreas alone certain portions of the proliferating 

 tubules become detached from the rest, forming islands of solid cords of 

 cells. These islands [of 

 Langerhans] were not found 

 in a human embryo of 28 mm. 

 (53 days) but have been 

 recorded at 54 mm. (73 days). 

 They are then round or oval 

 masses of cells rich in finely 

 granular eosinophilic proto- 

 plasm, which are still con- 

 nected with the developing 

 alveoli. Later they become 

 detached, and by the invasion 

 of capillaries of large diam- 

 eter they are irregularly sub- 

 divided into cords as seen in 

 Fig. 262. The islands are 

 said to appear first in the tail 

 and body of the pancreas, and 

 later in the head where they 

 are always relatively fewer. 

 In an early stage they are 



at the periphery of the lobules which are bounded by abundant connective 

 tissue, but subsequently they are surrounded by the proliferating alveoli 

 which reduce the connective tissue to interlobular septa (Fig. 263). It is 

 not now supposed that the islands arise from connective tissue, or that they 

 are produced in adult life by the degeneration of alveoli. The islands have 

 neither ducts nor lumen. Their secretion, which is internal, is received 

 by the blood vessels. It is essential for the metabolism of sugar as shown 

 by experiment. After removal of the pancreas, sugar appears in the urine; 

 on the other hand if the pancreatic ducts are tied the alveoli degenerate 

 but the islands remain intact, and sugar does not appear in the urine. 

 Thus the islands constitute an organ within but functionally independent 

 of the pancreas. 



FIG. 263. SECTION OP HUMAN PANCREAS, SHOWING SEV- 

 ERAL ISLANDS, f. 



a, Interlobular connective tissue containing an interlobular 

 duct, c; b, capillary; d, interlobular duct; e, alveoli. 

 (Radasch.) 



