1. An ectodermally lined depression under the root of the tail, adjacent to the terminal part of the embryonic hindgut; at its bottom, proctodeal ectoderm and cloacal endoderm form the cloacal plate. When this epithelial plate ruptures, the anal and urogenital external orifices are established. SYN: anal pit. 2. Terminal portion of the insect alimentary canal, extending from the pylorus (area of malpighian tubule attachment) to the anal opening; in certain diptera (flies) and other insects, the p. is divided into a tubular anterior intestine and an enlarged posterior intestine, or rectum, ending at the anus. [L. fr. G. proktos, anus + hodaios, on the way, fr. hodos, a way]
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proc·to·de·um or proc·to·dae·um .präk-tə-'dē-əm n, pl -dea or -daea -'dē-ə or -de·ums or -dae·ums the posterior ectodermal part of the alimentary canal formed in the embryo by invagination of the outer body wall
proc·to·de·al or proc·to·dae·al -'dē-əl adj
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n.
the site of the embryonic anus, marked by a depression lined with ectoderm. The membrane separating it from the hindgut breaks down in the third month of gestation. Compare stomodeum.
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proc·to·de·um (prok″to-deґəm) [proct- + Gr. hodaios pertaining to a way] an invagination of the surface ectoderm of the embryo at the point where later the anus is formed; called also anal pit.Medical dictionary. 2011.