At the end of the third embryonic week, the end of the hindgut expands to communicate with the anterior urinary bladder to form the cloaca. The caudal end of the cloaca is closed by a membrane of epithelial cells in the ectoderm, which becomes the cloacal membrane and separates it from the body. In the fourth week, the mesodermal folds between the cloaca and the hindgut are formed and grow caudally, and at the same time, the medial side of the two walls of the cloaca proliferates to form folds that grow into the cavity, and these form the urorectal septum, dividing the cloaca into two parts, the anterior and posterior, the former being the genital sinus of the bird and the latter being the rectum. At the same time, the cloacal membrane is also divided into two anterior and posterior parts, the former being the urogenital sinus and the latter being the anal membrane, which forms an anal concavity from the fifth week and gradually deepens close to the rectum. In the seventh and eighth weeks, the two membranes rupture one after another. After the rupture of the anal membrane, it connects with the rectum and forms the anus. By the 9th week of embryonic development, the development of the anorectum and its surrounding musculature is complete. In the fourth month of embryonic development, the perineum grows rapidly anteriorly and posteriorly, eventually moving the anus back to its usual position. In summary, anorectal development and formation is basically completed in the first 3 months of embryonic development, and prevention of anorectal malformations needs to be prevented in early pregnancy.