The testes, at an early period of foetal life, are placed at the back part of the abdominal cavity, behind the peritoneum, and each is attached by a peritoneal fold, the mesorchium, to the mesonephros.
See also mesentery mesovarium Mesorchium is the fibrous sheath which attaches vascular and avascular structures of spermatic cord together.
References
External links - "Inguinal Region, Scrotum and Testes: Coverings of the Testis"