The testicle is covered by the tunica albuginea, which is a dense, firm, inelastic, fibrous, white structure that forms the true outer coat of the testicle. It is lined by the tunica vasculosa, which is chiefly composed of a plexus of blood vessels. The tunica albuginea is about one and one-half millimeters thick throughout most of its extent, being thickest at the posterior margin of the gland under the epididymis, where it is invaginated and forms the mediastinum testis. It sends off centripetally directed processes, called trabeculae, which separate the interior of the testicle into compartments, within which lie the lobules of the testicle.

Tunica albuginea testis