Tunica albuginea of testis
The tunica albuginea is the fibrous covering of the testis. It is a dense blue-grey membrane, composed of bundles of white fibrous connective tissue, from which it derives its name :wiktionary:albuginea#Noun|albuginea, which interlace in every direction.
The tunica albuginea is covered by the tunica vaginalis, except at the points of attachment of the epididymis to the testis, and along its posterior border, where the spermatic vessels enter the gland.
The tunica albuginea is applied to the tunica vasculosa over the glandular substance of the testis, and, at its posterior border, is reflected into the interior of the gland, forming an incomplete vertical septum, called the mediastinum testis.
