Sentence:  In birds the rectum, at the termination of its canal, forms an oval or elongated pouch ... and then expands into a cavity, which has been named <WSD>cloaca</WSD>. 
Meaning of the word marked with <WSD> tags:  The duct in reptiles, amphibians and birds, as well as most fish and some mammals, which serves as the common outlet for urination, defecation, and reproduction.