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The rectum (from the Latin ''rectum intestinum'', meaning ''straight intestine'') is the final straight portion of the large intestine in some mammals, and the gut in others. The human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling) or the dentate line, again depending upon which definition is used.〔 In humans, the rectum is followed by the anal canal, before the gastrointestinal tract terminates at the anal verge. ==Structure== The rectum is a component of the lower gastrointestinal tract. The rectum is a continuation of the sigmoid colon, and connects to the anus. The rectum follows the shape of the sacrum, and ends in an expanded section called the ''rectal ampulla''. Unlike other portions of the colon, the rectum does not have taeniae coli. The rectum connects with the sigmoid colon at the level of S3, and connects with the anal canal as it passes through the pelvic floor muscles.〔 Supports of the rectum include: *Pelvic floor formed by levator ani muscles. *Waldeyer's fascia *Lateral ligaments of rectum which are formed by the condensation of pelvic fascia *Rectovesical fascia of Denonvillers, which extends from rectum behind to the seminal vesicles and prostate in front. *Pelvic peritoneum *Perineal body 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rectum」の詳細全文を読む スポンサード リンク
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