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Scrotum
The scrotum is an anatomical male reproductive structure that consists of a suspended sack of skin and smooth muscle that is dual-chambered, present in most terrestrial male mammals and located under the penis. One testis is typically lower than the other, which functions to avoid compression in the event of impact.〔Anthony F.Bogaert, "(Genital asymmetry in men )", ''Human Reproduction'' vol.12 no.1 pp.68–72, 1997. PMID 9043905.〕 The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which scrotal septum exists. It appears as a thin longitudinal line that runs front to back over the entire scrotum. The scrotum contains the external spermatic fascia, testes, epididymis, ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein and pampinform plexus. In humans and some other mammals, the scrotum becomes covered with pubic hair at puberty.
The scrotum is biologically homologous to the labia majora in females. Although present in most mammals, the external scrotum is absent in stream-lined marine mammals, such as whales and seals, as well as in some lineages of land mammals, such as the afrotherians, xenarthrans, and numerous families of bats, rodents, and insectivores.〔(【引用サイトリンク】url=http://www.nlm.nih.gov/medlineplus/ency/article/002296.htm )〕〔Lovegrove, B.G. 2015. "(Cool sperm: why some placental mammals have a scrotum. )" Journal of Evolutionary Biology. 27(5):801-814. doi: 10.1111/jeb.12373〕
== Structure ==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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