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 



■■■■«-' 



Fig. 184. — Frontal section through the region of the 



cloaca of a 5^-day chick embryo. 



an. F., Anal fokl. B. F., Bursa Fabricii. CI., Cloaca. 

 Coel., Coelome. Rect., Rectum. W. D., Wolffian duct. 

 X., Posterior angle of the body-cavity; the epitheHum 

 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 a 



