. The development of the chick; an introduction to embryology . nt., Entoderm 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 coprodseum represents the enlarged lower extremity of theembryonic large intestine. The bursa Fabricii is an entodermalstructure derived from the posterior portion of the embryoniccloaca. IV. The Development of the Liver axd Paxcreas The Liver. The anterior and posterior liver diverticula, de-scribed in Chapter VI, constitute the rudiments from which the 320 THE DEVELOPM
. The development of the chick; an introduction to embryology . nt., Entoderm 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 coprodseum represents the enlarged lower extremity of theembryonic large intestine. The bursa Fabricii is an entodermalstructure derived from the posterior portion of the embryoniccloaca. IV. The Development of the Liver axd Paxcreas The Liver. The anterior and posterior liver diverticula, de-scribed in Chapter VI, constitute the rudiments from which the 320 THE DEVELOPMENT OF THE CHICK substance of the liver is derived. A third diverticulum is dis-tinguished by Brouha as the right posterior diverticulum; this isan early outgrowth of the posterior diverticulum. Hepatic cylin-ders arise from 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. M. Fig. 187. — Reconstruction of gizzard, duodenum, and hepato-pancreatic ducts of a chick embryo ^ of 124 hours. (After Brouha.) D. ch., Ductus choledochus. D. cy., Ductus cys-ticus. D. h. cy., Ductus hepato-cysticus. D. h. d.,Dorsal or hepato-enteric duct. Du., bl., Gall bladder. Giz., Gizzard. Pa. d., Dor-sal pancreas. Pa. v. Right ventral V. s., Left ventral pancreas. end of the meatus, and it even encroaches on the sinus venosus, aswe have already seen; in the posterior part of the meatus venosus,on the other hand, the liver tissue is derived 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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