This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The name perineum in its broad sense is applied to the structures of the outlet of the pelvis, superficial to the levator ani muscle. In its restricted anatomical sense it is applied to the subpubic triangle as far back as a line joining the anterior portions of the tuberosities. In its clinical sense it is the space between the anus and scrotum in the male and anus and vulva in the female.
On examining the pelvic outlet the symphysis pubis is seen anteriorly with the descending rami of the pubes and ascending rami of the ischia on the sides, leading to the tuberosities. Posteriorly is seen the coccyx, with the spines of the ischia on each side comparatively close to it. The greater sacro-sciatic ligament runs from the sacrum to the tuberosity of the ischium, the lesser from the sacrum to the spine of the ischium. Taken together a diamond-shaped space is formed. In the female the pubic arch is wider, the tuberosities further apart, the spines of the ischia do not project so markedly inward, and the coccyx is more movable.
A line drawn from the anterior portion of one tuberosity to that of the opposite side passes 1.25 cm. (1/2 in.) in front of the anus, and divides the outlet into the urogenital triangle or perineum in front, and the anal triangle or ischiorectal region behind.
The urogenital triangle has the symphysis in front, the ischiopubic rami as far back as the anterior portion of the tuberosities on the sides, and a line joining the two behind. It is closed by a stout fibrous membrane called the triangular ligament.
The central point of the perineum is in the median line 2 cm. (3/4 in.) in front of the anus; it marks the posterior edge of the triangular ligament in the median line, and is the point of junction of the anteroposterior and transverse muscles.
There are four perineal fascias, viz.: (1) the superficial layer of the superficial fascia; (2) the deep layer of the superficial fascia, called also Colles's fascia; (3) the superficial layer of the deep fascia, or triangular ligament; and (4) the deep layer of the triangular ligament or pelvic fascia (Fig. 475).
The superficial layer of the superficial fascia is the subcutaneous fatty tissue, and is continuous with that of the surrounding parts and the dartos. When thick it makes operations on the deeper structures more difficult and sometimes impossible.
The deep layer of the superficial fascia or Colles's fascia is the fibrous under surface of the fatty superficial layer. Posteriorly it unites with the posterior edge of the triangular ligament; laterally it is attached to the ischiopubic rami; and anteriorly it is continuous with the under surface of the dartos of the scrotum, passes forward
Fig. 475. - The male perineum. The superficial perineal space is shown on the left and the deep perineal space on the right. ■ to form the suspensory ligament and fibrous sheath (Buck's fascia) of the penis, covers the spermatic cord, and is continuous with Scarpa's fascia (deep layer of the superficial fascia) of the abdomen.
The anterior layer of the triangular ligament is a firm fibrous membrane stretching from one tuberosity to the other, and attached to the ischiopubic rami on the sides forward to the pubic arch. Between its upper edge and the symphysis runs the dorsal vein of the penis, the dorsal artery and nerve piercing it a little lower and to the outer side; 2.5 cm. (1 in.) below the symphysis is the urethral opening with the opening for Cowper's ducts close to it below, and those for the vessels to the bulb close to it above. The superficial perineal vessels and nerves pierce its posterior edge. The posterior edge of the triangular ligament blends with the posterior edge of the deep layer of the superficial fascia (Colles).
The deep layer of the triangular ligament is a continuation downward of the pelvic fascia. It begins above on the inside of the pelvis, covering the obturator muscle as the obturator fascia; it then passes onto the levator ani muscles as the recto-vesical fascia. As the levator ani muscles do not meet in front, the gap between them is filled in at the median line below or posteriorly by the termination of the longitudinal fibres of the rectum (prerectalis muscles of Henle, recto-urethralis of Roux, Kalischer, Holl, Proust, and others - see page 438, Rectum), at the sides by the deep transverse perinei and compressor urethras muscles, and anteriorly by the continuation of the rectovesical fascia. From the deep transverse perinei muscles forward the rectovesical fascia is called the deep layer of the triangular ligament (Fig. 476).