The tunica albuginea is the fibrous envelope that extends the length of the corpus cavernosum penis and corpus spongiosum penis.

[1] The trabeculae of the tunica albuginea are more delicate, nearly uniform in size, and the meshes between them smaller than in the corpora cavernosa penis: their long diameters, for the most part, corresponding with that of the penis.

[citation needed] The external envelope or outer coat of the corpus spongiosum is formed partly of unstriped muscular fibers, and a layer of the same tissue immediately surrounds the canal of the urethra.

[2] The tunica albuginea is directly involved in maintaining an erection; that is due to Buck's fascia constricting the erection veins of the penis, preventing blood from leaving and thus sustaining the erect state.

[clarification needed][citation needed] This article incorporates text in the public domain from page 1250 of the 20th edition of Gray's Anatomy (1918)