The corpora cavernosa penis are surrounded by a strong fibrous envelope consisting of superficial and deep fibers. The superficial fibers are longitudinal in direction, and form a single tube which encloses both corpora; the deep fibers are arranged circularly around each corpus, and form by their junction in the median plane the septum of the penis.
This is thick and complete behind, but is imperfect in front, where it consists of a series of vertical bands arranged like the teeth of a comb; it is therefore named the septum pectiniforme.