DEEP FASCIAL LAYERS
Beneath Colles fascia, within the urogenital triangle, is a potential space termed the superﬁcial perineal compartment. Within this space, conﬁned by the inferior fascia of the urogenital diaphragm on its deep aspect, lie the bulbospongiosus, ischiocavernosus, and superﬁcial transverse perineal muscles. In addition, the bulb of the corpus cavernosum urethrae and the crura of the corpora cavernosa penis are found here. At the middle of the base of this triangle is the perineal body, a point of fusion between the muscles of the superﬁcial perineal compartment and the adjacent anal triangle posteriorly.
The deep fascia (Buck) of the penis is a distinct structure lying beneath the superﬁcial dartos or Colles fascia. Buck fascia is tenacious, dense, and whitish in appearance. It covers the penile corpora as a strong, ﬁbrous, tubelike envelope and is adherent to the underlying tunica albuginea of the penis, which immediately covers the paired cavernous bodies (see Plate 2-2). Buck fascia is distinct from the tunica albuginea that covers the paired corporal cavernosa and the spongiosal bodies, though no demonstrable space exists between these adjacent fascial layers. Near the base of each crus, Buck fascia becomes less distinct as it merges with the tunica albuginea. At this point, it is continuous with the deep suspensory ligament of the penis, which is attached to the symphysis pubis (see Plate 2-1).
Buck fascia originates distally at the penile coronary sulcus and forms a transverse intercavernous septum, which separates the penis into two compartments: the paired corpora cavernosa dorsally and the single spon- giosal body ventrally (see Plate 2-2, cross section). In the perineum, this fascia forms three compartments by covering each crus. Buck fascia covers the paired penile dorsal arteries and nerves and the deep dorsal vein (see Plate 2-2, cross section). In the perineum, Buck fascia lies beneath the reﬂected deep layer of Colles fascia that contains the bulbospongiosus and the ischiocavernosus muscles (see Plate 2-1).
Visualized in cross-sectional drawing on this page, a portion of Colles fascia (crural septum) spreads to cover the outer surfaces of the bulbospongiosus muscle and each ischiocavernosus muscle with the crura within. The cut margins of the crural septa, as they surround the ischiocavernosus muscles, are observed in the upper drawing. The deep layer of Colles fascia, shown extending posteriorly under the distal aspect of the bulbocavernosus muscle, is also illustrated. At this point, the deep layer of Colles fascia also turns backward around each penile crus and around the corpus spongiosum. This reﬂected layer blends with Buck fascia surrounding the crura.
Thus, in the urogenital triangle, four fascial layers cover the bulbous spongiosum and urethra. First is the perineal layer of Colles fascia external to the bulbospongiosus muscle. Beneath this is the deep extension of Colles fascia below the bulbospongiosus muscle, followed by Buck fascia and, ﬁnally, the tunica albuginea. Only three fascial layers cover each crus of the penis: Colles superﬁcial fascia overlying the ischiocavernosus muscles and Buck fascia beneath this muscle, which blends with the deep reﬂected layer of Colles fascia over the tunica albuginea.