316 THE DEVELOPMENT OF THE CHICK 
cloacal membrane, is the neck of the allantois, and dorsal to this, 
the large intestine. Though not shown in the figure, it may be 
noted that the Wolffian ducts open into the cloaca behind and 
dorsal to the opening of the rectum. 
The appearance of the cloaca in a longitudinal section does 
not, however, give an adequate idea of its form. The anterior 
portion of the cloaca which receives the rectum, stalk of the 
allantois and Wolffian ducts is expanded considerably in the 
lateral plane, and thus possesses a large cavity. The posterior 
2 
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Fig. 184. — Frontal section through the region of the 
cloaca of a 54-day chick embryo. 
an. F., Anal fold. B. F., Bursa Fabrici. Cl., Cloaca. 
Coel., Coelome. Reet., Rectum. W. D., Wolffian duct. 
X., Posterior angle of the body-cavity; the epithelium 
is invaginated and folded so as to simulate a glandular 
structure. 
portion, on the other hand, is greatly compressed laterally and 
the cavity is extremely narrow. During the fifth day the walls 
of this part of the cloaca become actually fused together, and 
its cavity obliterated, or rendered virtual only (Fig. 184). Thus 
the anterior part of the cloaca is prolonged backwards by 
