Pelvis and Perineum: Perineum and External Genitalia:Male

Pelvis and Perineum > Perineum and External Genitalia:Male > Study Aims
STUDY AIMS
At the end of your study, you should be able to:
Outline the general organization of the perineum
Describe the contents of the urogenital and anal triangles
Describe the central perineal tendon and perineal membrane
Outline the fascial layers and spaces of the perineum
Describe the anatomy of the scrotum
Describe the anatomy of the penis

Pelvis and Perineum > Perineum and External Genitalia:Male > Guides
GUIDE

5-7: Pelvis and Perineum: Perineum and External Genitalia: Male
Perineum (Plate 380 and Plate 381)
    General Organization
  • Narrow region between superior medial aspects of thigh ( Fig. 5-7-1)
  • With lower limbs abducted in lithotomy position, becomes a diamond-shaped area
  • Bounded by pelvic diaphragm superiorly and superficial fascia and skin inferiorly
  • Anal canal, urethra, and vagina pass through the perineum
  • Boundaries:
    • Anteriorly: Pubic symphysis
    • Posteriorly: Inferior sacrum and coccyx
    • Anterolaterally: Ischiopubic rami
    • Laterally: Ischial Tuberosities
    • Posterolaterally: Sacrotuberous ligaments
  • Divided into two triangles by imaginary line between ischial tuberosities
  • Posteriorly is anal triangle
  • Anteriorly is urogenital triangle
    Contents of Anal Triangle
  • Anal canal and anus
  • External and internal anal sphincters
  • Ischiorectal fossa
    Contents of Urogenital Triangle
  • Membranous and spongy urethra (males); distal urethra (females)
  • Vagina
  • Proximal erectile bodies of the penis (male) and vulva (female)
  • Attachment of the scrotum
    Central Perineal Tendon (perineal body)
  • Located at midpoint of the line dividing the urogenital from anal triangles
  • Mass of collagenous and elastic fibers
  • Deep to skin
  • Anterior to anal canal
  • Posterior to bulb of the penis (male) or vestibule (female)
  • Site of attachment for
    • Bulbospongiosus
    • Superficial transverse perineal muscles
    • Deep transverse perineal muscles
    • External anal sphincter
    • Fascicles of muscle from external sphincter urethrae and levator ani
    Perineal Membrane
  • Thin sheet of deep fascia
  • Runs between the two ischiopubic rami
  • Spans anterior pelvic outlet
  • Pierced by urethra and ducts of bulbourethral glands
  • Is attached to perineal body at midpoint of posterior margin
  • Thickened anterior margin = transverse perineal ligament
  • Superficial transverse perineal muscles
    • Lie superficial to (external to) perineal membrane
    • Extend from ischiopubic ramus on either side along posterior aspect of perineal membrane to attach to the perineal body
  • Deep transverse perineal muscles
    • Lie deep to (internal to) perineal membrane
    • Extend from ischiopubic ramus on either side along posterior aspect of perineal membrane to attach to the perineal body
  • Sphincter urethrae (external urethral sphincter)
    • Lies deep to (internal or superior to) perineal membrane
    • Circular fibers around membranous part of urethra in males
    • Anterior to deep transverse perineal muscles
  • Deep transverse perineal muscles and sphincter urethrae traditionally termed urogenital diaphragm
    Fascia and Spaces of the Urogenital Triangle
  • Superficial fascia of the urogenital triangle has two layers, similar to the abdomen
    • Superficial fatty layer
    • Deep membranous layer (Colles' fascia)
    • Superficial layer replaced in penis and scrotum by dartos layer (smooth or dartos muscle)
  • Membranous layer of superficial fascia
    • Posteriorly attached to posterior margin of perineal membrane and perineal body
    • Laterally attached to deep fascia (fascia lata) of superior medial thigh
    • Anteriorly is continuous with membranous layer of superficial fascia of abdomen (Scarpa's fascia)
  • Deep perineal fascia (Gallaudet's fascia)
    • Invests ischiocavernosus, bulbospongiosus, and superficial transverse perineal muscles
    • Fused to suspensory ligament of penis or clitoris
  • Superficial perineal space (pouch) (Plate 383)
    • Between membranous layer of superficial fascia and perineal membrane
    • Contains in males
      Bulb and crura of penis and associated muscles
      Proximal spongy urethra
      Superficial transverse perineal muscles
      Branches of internal pudendal vessels and pudendal nerves
    • Contains in females
      Crura of clitoris and associated muscles
      Bulbs of vestibule and associated muscles
      Superficial transverse perineal muscles
      Branches of internal pudendal vessels and pudendal nerves
      Greater vestibular glands
  • Deep perineal space (pouch) (Plate 383)
    • Lies between perineal membrane and pelvic diaphragm
    • Ischioanal fossae extend anteriorly into this space
    • Contains
      Membranous urethra
      External sphincter urethrae
      Bulbourethral glands: secrete clear mucous during sexual excitation, ducts descend through perineal membrane and terminate in spongy urethra
      Deep transverse perineal muscles
      Vessels and nerves
Male External Genitalia
    Scrotum ( Fig. 5-7-2 and Plate 387)
  • Sac derived from skin and superficial fascia of abdominal wall
  • Contains testes, epididymis and distal portion spermatic cord
  • Skin shows midline scrotal raphe = fusion of bilateral labioscrotal swellings in embryo
  • Dartos fascia
    • Continuation of deep membranous layer of superficial fascia of abdomen
    • Contains significant smooth muscle = dartos muscle
    • Extends inward, forming scrotal septum, separating right and left halves
  • Deep to dartos, tunics of spermatic cord (external spermatic, cremasteric and internal spermatic fascia form a fused layer around and external to tunica vaginalis
  • Supplied by external pudendal arteries and veins
  • Lymphatics drain to superficial inguinal lymph nodes
  • Innervated by
    • Anteriorly, ilioinguinal nerve and genital branch of genitofemoral
    • Posteriorly, posterior scrotal nerves (terminal branches of the pudendal) and perineal branches of the posterior femoral cutaneous nerves
    Penis (Plate 382)
  • Male organ of copulation
  • Composed of a body (shaft), root and glans
  • Body is
    • Anchored in superficial perineal space (pouch) and attached to perineal membrane
    • Contains three cylindrical masses of erectile tissue ( Fig. 5-7-3)
      1. paired corpora cavernosa in parallel on dorsal surface
      2. corpus spongiosum in midline of urethral surface (facing scrotum)
    • Each erectile body covered by a fibrous tunic albuginea
  • Corpora cavernosa
    • Diverge posteriorly to form the crura of the penis
    • Each crus attaches to the inferior surface of corresponding ischiopubic ramus, anterior to ischial tuberosity
  • Glans of the penis is the distal expansion of the corpus spongiosum: proximally it forms bulb
  • Membranous urethra pierces the perineal membrane and enters the bulb from above (so now is called spongy urethra) and terminates at external urethral meatus (at apex glans) ( Plate 381 )
  • Root of penis is formed by bulb and crura
  • Two muscles are associated with erectile bodies ( Table 5-7-1)
    • Bulbospongiosus muscle
    • Ischiocavernosus muscle
  • Body is surrounded by deep fascia (Buck's fascia), external to tunic albuginea
  • Skin of penis is connected to deep fascia by loose areolar connective tissue
  • At neck of the glans, the skin and connective tissue of the penis extends and a double-layered fold, the prepuce or foreskin
  • Vessels and nerves run on dorsum of penis
    • Between skin and deep fascia
    • Between deep fascia and tunica albuginea
  • Innervation
    • Dorsal nerve of the penis from the pudendal nerve
      Passes the length of the penis lateral to the dorsal artery on that side
      Lies beneath deep fascia
      Supplies skin and glans
    • Ilioinguinal nerve supplies skin of proximal shaft of penis
    • Erection controlled by parasympathetic nerves (pelvic splanchnic nerves), which relaxes smooth muscle in coiled arteries of penis supplying erectile bodies
  • Arterial supply
    • Dorsal arteries of penis from internal pudendal arteries run on either side of deep dorsal vein beneath deep fascia
    • Deep arteries from internal pudendal arteries
      Run distally within center of corpora cavernosa
      Highly coiled branches (helicine arteries) supply erectile tissue
    • Artery of bulb of penis from internal pudendal artery supplies posterior corpus spongiosum
    • External pudendal arteries supply skin of penis (branch of femoral artery).
  • Venous drainage
    • Deep dorsal vein of penis receives blood from venous plexus
      Drains to prostatic venous plexus and then to internal iliac/internal pudendal veins.
    • Superficial dorsal vein of penis drains to superficial external pudendal vein
  • Lymphatic drainage mainly to superficial inguinal nodes
Pelvis and Perineum > Perineum and External Genitalia:Male > Figures
FIGURES
Plate 381: Pelvis and Perineum—Perineum and External Genitalia: Male—Perineum and External Genitalia (Deeper Dissection)
Plate 387: Pelvis and Perineum—Perineum and External Genitalia: Male—Scrotum and Contents
Fig. 5-7-1: Dissection of male perineum to demonstrate the boundaries of the perineum. (From Gosling JA, Harris PF, Whitmore I, et al. Human Anatomy, 4th Edition Mosby, 2005, p. 214, Fig. 5.33)
Fig. 5-7-2: MRI scan. Coronal view through the male pelvis/perineum demonstrating the testes, scrotum and penile erectile tissue. (From Moses KP, Banks JC, Nava PB, et al. Atlas of Clinical Gross Anatomy. Mosby, 2005, p. 483, Fig. 38.14)
Fig. 5-7-3: Prosection of the penis demonstrating the position of the paired corpora cavernosa and corpus cavarum. The dorsal vein, nerve, and artery can also be identified. (From Gosling JA, Harris PF, Whitmore I, et al. Human Anatomy, 4th Edition Mosby, 2005, p. 217, Fig. 5.38)
Pelvis and Perineum > Perineum and External Genitalia:Male > Tables
TABLES

Table 5-7-1: Muscles of the penis
Muscle Proximal attachment Distal attachment Innervation Action
Bulbospongiosus Ventral surface of bulb of penis
Perineal body
Corpus spongiosus Deep branch of perineal nerve from pudendal nerve Compresses bulb of penis
Forces blood into body of penis during erection
Compresses outflow veins
Ischiocavernosus Inferior internal surface of ischiopubic ramus and ischial tuberosity Crus of penis Deep branch of perineal nerve from pudendal nerve Forces blood into body of penis during erection
Compresses outflow veins
(Courtesy of Noelle Granger, PhD)

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