Clinical anatomic study and embryological study of the pelvic outlet muscles

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With the development of clinical devices and skills in anorectal region, detailed anatomical information is required in these days. We performed detailed gloss anatomical research and compared with the images of ultrasound, and magnetic resonance imaging. We also performed histological analyses with muscles and connective tissue surrounding the anal canal. Histological analyses were also performed with mouse embryos to add the information concerning developmental processes.From these observations, we revealed the importance of longitudinal smooth muscle layer of the anal canal in human. The longitudinal muscle layer penetrated the external anal sphincter muscle. This structure is not observed in mice, and thought to be unique in human. After urorectal septum descend to separate the urogenital sinus and anorectal canal, it grew anteriorly, and contributed to the median raphe of external genitalia such as raphe of scrotum.