318 THE DEVELOPMENT OF THE CHICK 
shadow its final rupture. The lower end of the large intestine 
is perfectly solid, and higher up, somewhat vacuolated. (The 
solid stage begins on the seventh day.) The urinogenital ducts 
open into the urodzum above the solid end of the large intestine. 
It will be seen, therefore, that the urodzum is transformed into 
a passageway between the urinogenital ducts and the allantois, 
being closed anteriorly by the solid large intestine and posteriorly 
by the urodieal (cloacal) membrane. 
Fig. 185. — Photograph of the region of the cloaca in a median sagittal 
5 5 5D 
section of an 8-day chick. 
All., Allantois. An., Anus. B. F., Bursa Fabricii. caud. A., Caudal 
artery. Int., Intestine. N’ch., Notochord. p. P., Perianal papilla. Rect., 
Rectum. Ur’d., Urodzeum. 
During the twelfth and thirteenth days, the vacuoles in the 
upper part of the large intestine flow together and re-establish 
the cavity, but the lower end still remains closed by a solid plug 
of cells; immediately anterior to the latter the large intestine is 
dilated, and this apparently corresponds to the coprodzeum of 
