直腸・肛門の解剖学的特異性

The Anatomical Specificity of the Rectum and Anus

　下部腸管における直腸・肛門の解剖学的特異性は結腸を対照として比べると簡便である．個条書きにそれを挙げてみよう．なお関係する機能的な事項は編輯者の指示外だからなるべくふれない．

　Anatomic specificity of the rectum and anus should be fully taken into account in comparison with other divisions of the alimentary tract. The smooth muscular structure is very strong and, a few partly, muscle fibers arrange as in meshes of a basket. Different from the colon, the rectum does not rotate in embryonal life and shows no roving to sides. The arteries, veins, lymphatics and nerves reveal the arrangement in relation to such fixation, and some of them are intimately related with each side of walls of the pelvis. The distal end of the rectum has a most complicated hilus structure in the alimentary tract, and strong striated muscles participate in it. Besides, at least partly, muscle fibers of both kinds are mixed harmoniously with each other and constitute a stratum of the wall.

　At the anal canal, mucosa of the bowel is continuous with the skin via aoderm, and hemorrhoidal venous plexus, supplied by mesenterial and internal iliac arteries, freely communicate with both portal vein system and the systemic circulation. Similar structures are also found in lymphatics or nerves.

　Since their specificity is deeply related to various physiological functions as well as pathological changes, the rectum and the anus should not be put in the same category with other divisions of the bowel.