. The development of the chick; an introduction to embryology . of the rectum. Ly.,Nodules of crowded cells, probably primordia of lym-phoid structures in the wall of the large intestine. W. D.,Wolffian duct. the coproda?um represents the enlarged lower extremity of theembryonic large intestine. The bursa Fabricii is an entodermalstructure derived from the posterior portion of the embryonic;cloaca. IV. The Development of the Liver and Pa\cre.\s The Liver. The anterior and posterior liver diverticula, de-scribed in Chapt(>r VI, constitute the rudiments from which tlie ,S20 THE DEVELOPMENT OF
. The development of the chick; an introduction to embryology . of the rectum. Ly.,Nodules of crowded cells, probably primordia of lym-phoid structures in the wall of the large intestine. W. D.,Wolffian duct. the coproda?um represents the enlarged lower extremity of theembryonic large intestine. The bursa Fabricii is an entodermalstructure derived from the posterior portion of the embryonic;cloaca. IV. The Development of the Liver and Pa\cre.\s The Liver. The anterior and posterior liver diverticula, de-scribed in Chapt(>r VI, constitute the rudiments from which tlie ,S20 THE DEVELOPMENT OF THE CHICK sul)stan(o of the liver is derived. A third diverticvilum is dis-tinguished by Hrouha as the right posterior diverticvihiin; this isan early outgrowth of the posterior diverticulum. Hepatic cylin-ders arise fiotn both primary diverticula at an early stage, andthese, branching and anastomosing, soon form a basket-work ofliver tissue around the intermediate portion of the meatus anterior diverticulum alone extends forward to the anterior. Fi(i. 1S7. - Reconstruction of fjizzard, duodenum,and hepato-pancreatic ducts of a chick embryoof 124 hours. (After Brouha.)I), ch., Ductus choledochus. D. Ductus cys-ticus. D. h. cy., Ductus hei)ato-cysticus. D. h. or hepato-enteric duct. Du., 1)1., (!all l)la(lder. (iiz., Gizzard. Pa. Dor-sal pancreas. Pa. v. d., Hifiht ventral V. Left ventnd pancreas. end of the meatus, and it even encioaches on the sinus venosus, aswe have already seen; in the posterior part of the meatus v^enosus,on the other hand, the liver tissue is deriv^ed entirely from theposterior diverticulum. The mesenchyme in the interstices ofthe hepatic framework is replaced almost immediately by blood- ALIMENTARY TRACT AND ITS APPENDAGES 321 vessels that empty into the meatus, and thus appear as branchesof the latter. The gall-bladder is a very early formation, arising from thehindermost portion of the poster
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