VI.J THE PANCKEAS. 181 



each solid cylinder to represent a duct with its lumen 

 almost, but perhaps not quite, completely obliterated. 



During the fifth day, a special sac or pouch is deve- 

 loped from the right primary diverticulum. This pouch, 

 consisting of an inner coat of hypoblast, and an outer of 

 mesoblast, is the rudiment of the gall-bladder. 



The Pancreas arises nearly at the same time as the 

 liver in the form of an almost solid outgrowth from the 

 dorsal side of the intestine nearly opposite but slightly 

 behind the hepatic outgrowths (Fig. 60, f). Its blind 

 end becomes somewhat enlarged and from it numerous 

 diverticula grow out into the passive splanchnic meso- 

 blast. 



As the ductules grow longer and become branched, 

 vascular processes grow in between them, and the whole 

 forms a compact glandular body in the mesentery on 

 the dorsal side of the alimentary tract. The primitive 

 outgrowth elongates and assumes the character of a duct. 



On the sixth day a new similar outgrowth from 

 the duodenum takes place between the primary diver- 

 ticulum and the stomach. This, which ultimately 

 coalesces with its predecessor, gives rise to the second 

 duct, and forms a considerable part of the adult pan- 

 creas. A third duct is formed at a much later period. 



The Thyroid body. The thyroid body arises at the end of 

 the second or beginning of the third day as an outgrowth from 

 the hypoblast of the ventral wall of the throat opposite the 

 point of origin of the anterior aortic arch. It has at first the 

 form of a groove extending forwards up to the future mouth, and 

 in its front part extending ventrally to the epiblast. It has not 

 been made out whether the whole groove becomes converted into 

 the permanent thyroid. By the fourth day it becomes a 

 solid mass of cells, and by the fifth ceases to be connected 



