392 FREDERIC T. LEWIS 



over Helly's interpretation is not applicable to the pig embryo 

 shown in fig. 3. 



While the ventral pancreas of the pig is passing through its 

 transient paired stage, the dorsal pancreas is also represented 

 by a pair of epithelial proliferations (fig. 2, c, d) . These are plate- 

 like thickenings, and not round buds as in the case of the ventral 

 pancreas. The plate on the right soon becomes larger than that 

 on the left (fig. 3). At this stage (4.5 mm.), the dorsal wall of 

 the intestine has become thickened and forms a part of the dorsal 

 pancreas. Later, as in the 6.0 mm. embryo shown in fig. 11, the 

 entire structure is an asymmetrical bi-lobed mass swinging toward 

 the right. In embryos of 10 and 12 mm., the bi-lobed condition 

 is generally clearly seen where the duct enters the duodenum (fig. 

 8), but anteriorly these lobes are lost in the compact mass which 

 turns toward the right (fig. 7, P. d.). 



The bi-lobed form of the dorsal pancreas of pig embryos has 

 been recognized by Wlassow and Volker, but its paired origin has 

 not been previously recorded. In the sheep, however, Stoss 

 observed the parallel development of the dorsal and ventral pan- 

 creases, both of which he described as paired. Felix, Brachet, and 

 Helly have denied the paired origin of the dorsal pancreas, which, 

 indeed, is not apparent in the rabbit, or in other mammals in which 

 the dorsal margin of the intestine is thickened from the first. But 

 in pig embryos the parallelism is strikingly shown. Both the 

 dorsal and ventral pancreases pass through a transient paired 

 stage; both become median structures which are more or less 

 bi-lobed, and both develop predominantly on the right side. 



The ventral pancreas in pig embryos may extend wholly toward 

 the right side, as seen in figs. 4 and 6, from embryos of 5.1 mm. 

 and 10 to 12 mm. respectively. In the younger specimen, the 

 upper part of the pancreas is subdivided by a groove into left- 

 anterior and right-posterior divisions. If these lobes are due to 

 the fusion of the primary buds, it is evident that the right bud 

 has produced the greater part of the ventral pancreas. In the 

 older specimen (fig. 6), there is no trace of a left lobe. But in 

 other cases, as shown in figs. 5 and 7, from embryos of 6.0 mm. and 

 10 to 12 mm. respectively, both lobes are well defined; in both 



