Lateral view, superficial side

Lateral view, deep side

The fascial sac or tunica vaginalis (translated this means "ensheathing coat") is formed from the aponeuroses of the abdominal muscles when the testis descends through the inguinal canal on its way to the scrotum.  In addition to the aponeuroses peritoneum is included in the fascial sac, and in fact it is the peritoneum that is technically the tunica vaginalis, even though these terms are used interchangeably.  Within the the fascial sac is a cavity containing fluid.  Occasionally when the testis becomes inflamed, fluid builds up in this cavity also.  A piece of material connects the testis to the fascial sac - this is the remnant of the gubernaculum.  Remember that the remnants of the gubernaculum in the female make up the round ligaments of the ovary and uterus.