ALIMENTARY TRACT AND ITS APPENDAGES 319 
the adult cloaca. Even on the seventeenth day the large intes- 
tine appears to be still closed at its lower end, and the urodeal 
membrane still persists as a plug of vacuolated cells. (Gasser.) 
Both plugs must, however, disappear soon after. 
It would thus appear that the urodzeum only of the adult 
cloaca corresponds to the embryonic cloaca; the proctodzeum is 
certainly derived from an ectodermal pit, and it is probable that 
Fia. 186. — Chick embryo of 11 days, sagittal section 
through the region of the cloaca. Reconstructed from 
several sections. (After Minot.) 
All’., Ascending limb of the allantois. AIl”., Descend- 
ing limb of the allantois. An., Analinvagination. An. pl., 
Urodeal membrane. Art., Umbilical artery. B. F., 
Bursa Fabricii. b. f., Duct of the bursa. Clo., Cloaeca. 
Ee., Ectoderm. Ent., 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 coprodeum represents the enlarged lower extremity of the 
embryonic large intestine. The bursa Fabricii is an entodermal 
structure derived from the posterior portion of the embryonic 
cloaca. 
IV. Tuer DEVELOPMENT OF THE LIVER AND PANCREAS 
The Liver. The anterior and posterior liver diverticula, de- 
scribed in Chapter VI, constitute the rudiments from which the 
