The hindgut extends from the midgut to the cloacal membrane. It gives rise to the distal third of the transverse colon, descending colon, sigmoid, rectum and the upper part of the anal canal.
The teminal portion of the hindgut enters into the cloaca covered by the cloacal membrane. The growth of the urorectal septum divides the cloaca into the primitive urogenital sinus anteriorly and the anorectal canal posteriorly. By the end of the 6th week, the urorectal septum reaches the cloacal membrane, dividing it into the urogenital and anal membranes.
The mesenchymal swelling around the anal membrane forms the proctodeum (anal pit). In the 9th week, the anal membrane ruptures. The upper part of the anal canal is endodermal in origin, while the lower third is of the ectodermal origin. |
