mesorchium mesorchium 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. mesorchiumschematic drawing of a cross-section through the vaginal process. 1 testicle, 2 epididymis, 3 mesorchium, 4 lamina visceralis of tunica vaginalis, 5 lamina parietalis of tunica vaginalis, 6 cavum vaginale, 7 mesepididymis, 8 fascia spermatica internaanatomical terminology