228 (JEORGE W. CORNER 



are iiiitloubtedly joroduced in a way exactly like those of the blood- 

 \'ascular system, as demonstrated by the work of Evans ('08, 

 '09) and others. Just as a blood-capillary supplying the embry- 

 onic arm-bud or kidney may for some reason persist after its 

 time and form an accessory brachial artery or renal vein; so at 

 the time of appearance of the pancreatic duct, varying physical 

 forces may lead the new channel through one or another mesh 

 of the plexus shown in figure 7, and in this way any imaginable 

 variation may be produced, even loops and spirals, while the 

 external form of the pancreas remains without change. 



In the 60 mm. stage we find signs of the next step in develop- 

 ment (fig. 10). From the sides of the anastomosing tubules 

 grow out many short, narrow twigs, which do not anastomose, 

 and occasionally branch at their tips. In foetuses of 80 mm. 

 (fig. 12), these branching tubules have grown into complex trees, 

 forming the whole organ. Figure 13 A, represents a fortunate 

 injection at the 140 mm. stage, made as described, by inserting 

 a fine hollow glass needle into the duct just outside the duodenum 

 at the point indicated (n). The India ink has completely filled 

 the ducts, which extend in a branching system all through the 

 organ. In the detailed drawing, figure 13 B, the terminal branches 

 are shown in their full complexity, and by comparing this stage 

 with figure 7, one gets a striking impression of the total change 

 which the ducts have undergone. 



The former thick plexus has disappeared, and only a few anas- 

 tomoses remain; they can be found as late as 110 mm., after 

 which they either disappear entirely or are obscured by the for- 

 est of acini and ductules. Perhaps they remain in pai"t to form 

 that curious network found by Bensley ('11) about the larger 

 ducts and throughout the pancreas, if his observations upon the 

 guinea-pig hold good for other animals, as we may suppose they 

 do. Why a rapidly developing organ should suddenly quit one 

 manner of growth and take another, is altogether obscure. Per- 

 haps the anastomosing plexus represents a vestigial tendency of 

 the pancreatic anlagen, correlated with their close embryological 

 relation to the liver, to be discarded in accordance with the 

 demands of new function. It is obviously unnecessary for tu- 



