. Surgery, its principles and practice . Fig. 83. Fig. 84. These malformations are due to the fact that the rectum and anusare developed separately, the former from ectodermal and mesodermal (internal) structures,and the latter from epi-dermal (external). Thestudy of embryology hasadded largely to theunderstanding of thenature and classificationof congenital rectal de-fects. Very early indevelopment the lowerportion of the primitivegut connects with theneurenteric canal (post-anal gut), but this junc-tion speedily disappears,leaving the intestineclosed behind it andterminating in a cloacacommo
. Surgery, its principles and practice . Fig. 83. Fig. 84. These malformations are due to the fact that the rectum and anusare developed separately, the former from ectodermal and mesodermal (internal) structures,and the latter from epi-dermal (external). Thestudy of embryology hasadded largely to theunderstanding of thenature and classificationof congenital rectal de-fects. Very early indevelopment the lowerportion of the primitivegut connects with theneurenteric canal (post-anal gut), but this junc-tion speedily disappears,leaving the intestineclosed behind it andterminating in a cloacacommon to it and theurachus. During the secondmonth the perineal par-tition divides this dilata-tion into the urogenitalsegment and the the same time a de-pression at the anal site(proctodeum) forms inthe skin, and lined byepiderm, extends in-ward to meet the blindend of the ectodermaltube, into which itopens. In arrested or irreg-ular development of oneor more of the severalstructures we have thebasis for the variousmalformations,
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