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Ischiopagi comes from the Greek word ''ischio-'' meaning hip (ilium) and ''-pagus'' meaning fixed or united. It is the medical term used for conjoined twins (Class V) who are united at the pelvis. The twins are classically joined with the vertebral axis at 180°. However, the most frequent cases usually structures the ischiopagus twins with two separate spines forming a lateral angle smaller than 90°. The conjoined twins usually have four arms; two, three or four legs; and typically one external genitalia and anus.〔(Duplicata incompleta, dicephalus dipus dibrachius ), 2008-06-20〕 It is mostly confused with pygopagus where the twins are joined ventrally at the buttocks facing away from each other, whereas ischiopagus twins are joined dorsally at the sacrum and coccyx. Parapagus is also similar to ischiopagus; however, parapagus twins are joined side-by-side whereas ischiopagus twins typically have spines connected at a 180° angle, facing away from one another. 〔http://phreeque.tripod.com/conjoined_twins.html〕 ==Classification== Ischiopagus Dipus: This is the rarest variety with the twins sharing two legs with no lower extremities on one side. Ischiopagus Tripus: This is the most common variety. These twins share three legs, the third leg is often two fused legs, or is non-functioning. The twins also usually share only one set of external genitalia. Ischiopagus Tetrapus/Quadripus: This variety has the twins at a symmetrical continuous longitudinal axis with their area of union not broken anteriorly. The axes extends in a straight line but in opposite directions. The lower extremities are oriented at right angles to the axes of the thorax and the adjacent limbs near the union of the ischium belong to the opposite twin.〔 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「Ischiopagi」の詳細全文を読む スポンサード リンク
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