The corpus cavernosum penis is one of a pair of sponge-like regions of erectile tissue which contains most of the blood in the penis during penile erection. This is homologous to the corpus cavernosum clitoridis in the female; the body of the penis contains erectile tissue in a pair of corpora cavernosa (literally "cave-like bodies"), with a recognizably similar structure. The paired corpora cavernosa contain erectile tissue and are each surrounded by the tunica albuginea, a dense fibrous sheath of connective tissue with relatively few elastic fibers. The two corpora cavernosa and corpus spongiosum are three expandable erectile tissues along the length of the penis which fill with blood during penile erection. The two corpora cavernosa lie along the penis shaft, from the pubic bones to the head of the penis, where they join. These formations are made of a sponge-like tissue containing irregular blood-filled spaces lined by endothelium and separated by connective tissue septa.