= Solution
\b[<Cowper's glands> are the paired <bulbourethral glands>, deep to the <perineal membrane> on either side of the membranous <urethra>.] The relevant dissection is of the male anterior <perineum>, or <urogenital triangle>. A broad exposure reveals structures at different lateral positions; they are not all piled one above another along a single central line.
From superficial to deep, the principal layers and contents are:
* \b[<Skin> and superficial <fascia>.] The superficial fascia includes a fatty layer and a deeper membranous layer, <Colles' fascia>. The latter attaches laterally to the ischiopubic rami and posteriorly towards the posterior border of the <perineal membrane> and <perineal body>; anteriorly it is continuous with fascia of the scrotum and lower abdominal wall. Superficial vessels and <nerves> accompany these layers. Cutaneous arterial supply includes branches of the <perineal artery> and, more anteriorly, contributions associated with the external pudendal circulation.
* \b[The superficial perineal compartment.] Removing the membranous fascia exposes the superficial pouch and the investing fascia over its <muscles>. Centrally, <bulbospongiosus> covers the bulb of the penis and proximal <corpus spongiosum>. On either side, <ischiocavernosus> covers a crus of the penis. Posteriorly, the <superficial transverse perineal muscle> runs towards the <perineal body>. Older descriptions call these the accelerator urinae, erector penis and transversus perinei respectively. The names should be matched to the structures rather than counted as additional <muscles>.
* \b[Superficial perineal vessels.] The <perineal artery>, a branch of the <internal pudendal artery>, supplies this region and gives posterior scrotal and muscular branches; accompanying <veins> drain it. These vessels lie in relation to the pouch and its <muscles>, rather than constituting a complete vascular sheet. The bulb and crura are the associated <erectile tissues>, not additional membranes.
* \b[The <perineal membrane>.] This dense fibrous sheet spans the anterior pelvic outlet between the ischiopubic rami. It is the structure traditionally described as the triangular ligament's inferior layer. It is pierced by the <urethra> and by the ducts of the <bulbourethral glands>, as well as related vascular passages. The <artery of the bulb of the penis> passes to the bulb in close relation to the membrane. The deep and dorsal penile arterial routes lie more anteriorly; they should be identified where the exposure reaches them rather than imagined to cross every central dissection plane.
* \b[The deep perineal structures.] Beyond the <perineal membrane> are the <external urethral sphincter> complex, traditionally described deep transverse perineal fibres, the membranous <urethra> and the <bulbourethral glands>. The glands lie in close relation to sphincteric <skeletal muscle>. Their ducts run forwards through the <perineal membrane> and open into the bulbar <urethra>, so the position of a duct's opening is not the position of its gland.
The superficial <muscles>, erectile bodies and pudendal branches identify the shallow compartment; the <perineal membrane> separates it from the gland-bearing deeper region.<Anatomy, Abdomen and Pelvis: Superficial Perineal Space (StatPearls)>[Structure and Function; Blood Supply and Lymphatics; Muscles]{ref} The deep space contains the sphincter complex and male <bulbourethral glands>, with their ducts traversing the membrane.<Anatomy, Abdomen and Pelvis: Deep Perineal Space (StatPearls)>[Introduction; Structure and Function; Blood Supply and Lymphatics]{ref}
The main <internal pudendal vessels> themselves run laterally in the <pudendal canal>, in relation to the fascia over <obturator internus>, before their terminal distribution. A median approach to a gland does not necessarily expose their whole trunks. The <deep dorsal vein of the penis> has a distinct anterior route beneath the pubic arch and should not be confused with the small accompanying perineal <veins>. These positional qualifications are necessary for an accurate enumeration of the vessels one may meet.
Nineteenth-century descriptions often arranged the deep structures as a <urogenital diaphragm> enclosed between two neat fascial layers, the superior and inferior layers of the triangular ligament. Modern dissection finds a more complex sphincteric and connective-tissue arrangement. The historically named layers explain the older vocabulary, but the <perineal membrane> and surrounding <muscles> should not be made into a fictitious uniform sandwich. Nor does reaching the <bulbourethral glands> require dissecting through the whole <pelvic diaphragm> above them.
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