ALIMENTARY TRACT AND ITS APPENDAGES 325 



final terminations of the buds form the secreting and the inter- 

 mediate portions the various intercalated and excretory ducts 

 that form a branching system opening into the main ducts. 



The successive stages in the development of the pancreas 

 may be stated thus (following Brouha) : At 124 hours the two 

 ventral pancreatic ducts pass anteriorly and a little to the left, 

 crossing the cephalic hepatic duct which lies between them. 

 They are continued into ramified pancreatic tubes which already 

 form two considerable glandular masses. The right ventral 

 pancreas is united by a very narrow bridge to the dorsal pancreas, 

 and the latter is moulded on the left wall of the portal vein, 

 while its excretory duct has shifted on the left side of the duo- 

 denum nearer the duct us choledochus. At 154 hours the duct of 

 the dorsal pancreas is still nearer to the others, and the three pan- 

 creatic ducts enter a single glandular mass, the dorsal portion of 

 which, derived from the primitive dorsal pancreas, is moulded on 

 the left wall of the portal vein, and is continued into a smaller ven- 

 tral portion formed by the fusion of the two ventral pancreases. 



Subsequently, the pancreatic lobes fill up the duodenal loop 

 (Figs. 179 and 180), and elongate with this so as to extend from 

 one end of it to the other in the adult; the three ducts open 

 near the termination of the duodenum (end of distal limb) 

 beside the two bile ducts. 



V. THE RESPIRATORY TRACT 



The origin of the laryngotracheal groove and the paired 

 primordia of the lungs was described in Chapter VI. At the stage 

 of 36 somites the laryngotracheal groove includes the ventral 

 division of the postbranchial portion of the pharynx, which is 

 much contracted laterally so as to convert its cavity into a deep 

 and narrow groove. This communicates posteriorly with right 

 and left finger-shaped entodermal diverticula (the entodermal 

 lung-primordia) extending into the base of the massive pear- 

 shaped mesodermal lung-primordia attached to the lateral walls 

 of the oesophagus. The mesodermal lung-primordia are con- 

 tinuous with the accessory mesenteries, as described in Chapter XI; 

 and by them attached to the septum transversum. 



Bronchi, Lungs and Air-sacs. The primitive entodermal 

 tubes form the primary bronchi, in which two divisions may be 

 distinguished on each side, viz: a part leading from the end of 



