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THE MERCK MANUAL, Sec. 3, Ch. 35, Anorectal Disorders |
 | | The anal canal is derived from invagination of the ectoderm, and the rectum, from invagination of the entoderm. |
 | | The sphincteric ring encircling the anal canal is composed of the fusion of the internal sphincter, the central portion of the levators, and the components of the external sphincter. |
 | | Lymphatics from the anal canal pass to the internal iliac nodes, the posterior vaginal wall (in women), and the inguinal nodes, whereas lymphatic return from the rectum is along the superior hemorrhoidal vascular pedicle to the inferior mesenteric and aortic nodes. |
| www.merck.com /pubs/mmanual/section3/chapter35/35a.htm (433 words) |
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