Dissector Answers - Male Reproductive Anatomy

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Trace the skeletal and ligamentous boundaries of the perineum, and define the anal and urogenital triangles.
  2. Identify the superficial features of the external genitalia in the male.
  3. Describe the structure, contents, and course of the pudendal canal.
  4. Trace the branching pattern of the internal pudendal vessels and the pudendal nerve.
  5. Identify the parts of the male urethra.
  6. Identify the components of the external genital organs and give the homologues in each of both sexes.
  7. Describe structure and function of the erectile bodies.
  8. Identify the muscles and fasciae of the perineum and their functions.
  9. Trace the nerve and blood supply to the external genital organs and the muscles of the perineum.
  10. Trace the lymphatic drainage of the perineum.
  11. Trace the continuity of the abdominal peritoneum with that of the pelvic cavity.
  12. Describe the relationships of the bladder to other pelvic organs.
  13. Identify the testis, its coverings, and tubules, and account for the difference in location between gonads in the two sexes.
  14. Trace the entire course of the ductus deferens from the epididymis to its ampulla; note its relationship to the ureter.
  15. Identify the seminal vesicle and demonstrate the formation and course of the ejaculatory duct.
  16. Identify the prostate gland and describe the special features of the prostatic urethral wall.

Learning Objectives and Explanations:

1. Trace the skeletal and ligamentous boundaries of the perineum, and define the anal and urogenital triangles. (W&B 519, N 379A, 379B, TG 6-24A, 6-24B)

Officially, the perineum is the outlet of the pelvis. (Used more loosely, it can refer to the area of skin between the anus and the posterior part of the external genitalia.) It is diamond-shaped, and can therefore be divided into two isosceles triangles by a line drawn between the ischial tuberosities. The anterior, or urogenital triangle has as its apex the pubic symphysis, with the ischiopubic rami as equal sides, and our imaginary line as the base. The posterior, or anal triangle is upside-down, with our line again as the base, the sacrotuberal ligaments as the equal sides, and the coccyx as the apex. (peri + inan ("to empty out" in Greek))

You really need to think about this in 3-D because, although drawn two-dimensionally from an inferior point of view it looks like the coccyx, anus, vagina, and pubic symphysis are all coplanar, they are not.

2. Identify the superficial features of the external genitalia in the male. (W&B 519-522, N 351, 377, 382, 387, 390, 398, TG 6-02, 6-25A, 6-25B, 6-31)

Sorry to cop out and paste in the tables, but there is little connectivity or functionality that needs to be explained. It is pretty much a "these are the things you should know about" situation.

Male:
Organ Location/Description Notes
glans penis expanded distal end of the corpus spongiosum which caps the ends of the corpora cavernosa the fossa navicularis is an expanded portion of the penile urethra that occurs in the glans
prepuce fold of smooth skin extending over the glans penis also "foreskin"
scrotum sac of hair-covered skin containing the testis in the scrotum the fatty and membranous layers of the superficial fascia (as seen in the lower abdominal wall) are fused to form the tunica dartos scroti

Female:
Organ Location/Description Notes
clitoris combination of 3 erectile bodies: glans clitoris and 2 corpora cavernosa clitoris clitoris is covered by smooth skin
glans clitoridis expanded distal end of the corpus spongiosum which caps the ends of the corpora cavernosa  
prepuce fold of smooth skin extending over the glans clitoris the anterior divisions of the labia minora combine to form the prepuce of the clitoris
hymen thin, usually incomplete septum at the inferior vaginal orifice the hymen is the remnant of the urogenital septum of the embryo, and the hymeneal caruncles are remnants of the hymen
labia majora fat-filled elevations of hair-covered skin lying on either side of the vestibule of the vagina labia majora are joined across the midline by the anterior and posterior labial commissures; they blend into each other anteriorly to form the mons pubis
labia minora paired folds of hairless skin located medial to the labia majora and extending posteroinferiorly from the clitoris the anterior end of each labium minus divides: the anterior division of each labium forms the prepuce of the clitoris and the posterior division of each labium forms the frenulum of the clitoris
vagina part of the female genital canal located between the vestibule and the cervix vaginal fornices surround the cervix; the word "vagina" is derived from the Latin word for sheath
vestibule of the vagina region inferior to the hymen/hymeneal caruncles and between the labia minora vestibule of the vagina contains the external urethral orifice, the opening of the vagina and the openings of the greater vestibular glands
uterus hollow muscular organ within which the fertilized ovum develops; normally lies anteverted posterosuperior to the bladder uterus is anteflexed (curved anteroinferiorly) at the uterine isthmus; the fundus is the part superior to the entrance of the uterine tubes and it normally lies anterosuperiorly; the body meets the cervix at a constricted area called the isthmus; the cervix projects into the vagina
3. Describe the structure, contents, and course of the pudendal canal. (W&B 524-526, N 404, 405, 411, 413, TG 6-28A, 6-28B)

The pudendal canal extends from the lesser sciatic foramen, where its contents enter the perineum, to the posterior edge of the perineal membrane. It contains the internal pudendal artery, internal pudendal vein, and the pudendal nerve.

4. Trace the branching pattern of the internal pudendal vessels and the pudendal nerve. (W&B 524-526, N 404, 405, 411, 413, TG 6-29A, 6-29B, 6-30A, 6-30B)

The internal pudendal artery gives off the following branches. The internal pudendal vein receives analogous tributaries.

The pudendal nerve has the following branches:

5. Identify the parts of the male urethra. (W&B 542-543, N 369, 379, 384, 385, TG 6-08A, 6-08B, 6-09A, 6-09B, 6-10A, 6-10B)

The female urethra is about four centimeters long and is entirely "membranous urethra". The male urethra is longer than the female urethra, and is divided into three parts: membranous, prostatic, and penile (spongy) urethra. (See Pelvis & Pelvic Viscera Dissector Answers.)

6. Identify the components of the external genital organs and give the homologues in each of both sexes. (W&B 543-551, 403-413, N 379A, 379B, 382A, 382B, 418A, 418B, TG 6-25A, 6-25B, 6-27A, 6-27B)
Female Male
vestibular bulbs corpus spongiosum
greater vestibular glands bulbourethral glands
urethral and paraurethral glands prostate gland
glans clitoris glans penis
prepuce of clitoris prepuce of penis
corpus of clitoris corpus (shaft) of penis
labia minora penoscrotal raphe
labia majora scrotum
7. Describe structure and function of the erectile bodies. (W&B 520-523, 527-528, N 379A, 379B, 381, 382A, 382B, TG 6-27A, 6-27B, 6-32)

The three primary erectile bodies of the penis are the two corpora cavernosa and the corpus spongiosum. These structures are surrounded by a dense tunica albuginia such that, when they are engorged with blood, the penis becomes erect. The glans penis, the expanded cap of the corpus spongiosum, remains more malleable during erection because it has a much thinner tunica albuginea than the rest of the components of the penis.

The corpora cavernosa are rooted in the perineum by two crura of the penis. Each crus is attached to the ischiopubic ramus. The corpus spongiosum is rooted as the bulb of the penis, which is attached to the perineal membrane, and receives the membranous urethra as it transverses the membrane.

There are homologous structures in the female. The clitoris contains corpora cavernosa as its erectile tissue. Like in the male, each crus is attached to the ischiopubic ramus and perineal membrane. Instead of a corpus spongiosum, the female has two vestibular bulbs, which lie along the sides of the vestibule, and also expand as the glans clitoris to cap the distal ends of the corpora cavernosa.

8. Identify the muscles and fasciae of the perineum and their functions. (W&B 524-525, N 404, 405, 411, 413, TG 6-29, 6-30A, 6-30B)

The perineal membrane stretches between the two ischiopubic rami and serves as an anchor for the erectile bodies and their associated muscles. It also divides the perineum into superficial and deep spaces, sometimes referred to as "pouches". The perineal membrane is set at an angle (as are the ischiopubic rami), so that the superficial perineal pouch is anteroinferior to the perineal membrane while the deep perineal pouch is posterosuperior to the perineal membrane. The best way to consider these structures is to look at the tables:

perineal membrane (N379, N381, TG6-27A, TG6-27B) membrane stretching across the urogenital triangle attaching to both ischiopubic rami perineal membrane is pierced by the urethra and branches of the pudendal neurovascular bundle (and vagina in female)
perineal body (N379, TG6-27A) fibrous connective tissue in the midline between the vestibule of the vagina and the anus many of the muscles of the perineum attach at or to the perineal body, including the transverse perineal muscles, bulbospongiosus, and external anal sphincter; the male version is often called the central tendinous point

Muscles
Muscle Origin Insertion Action Innervation Artery Notes Image
bulbospongiosus, in male (N379, N382, TG6-27A, TG6-27B) central tendinous point and the midline raphe on the bulb of the penis perineal membrane, dorsal surface of the corpus spongiosum, deep penile fascia compresses the bulb of the penis, compresses the spongy urethra deep branch of the perineal nerve (from pudendal nerve) perineal a. expels the last drops of urine from urethra; expels semen during ejaculation
ischiocavernosus (N379, N382, TG6-27A, TG6-27B) medial surface of the ischial tuberosity and the ischiopubic ramus corpus cavernosum and crus of the penis/clitoris compresses the corpus cavernosum deep branch of the perineal nerve (from pudendal nerve) perineal a. ischiocavernosus m. is closely applied to the surface of the crus penis/clitoris
sphincter urethrae, in male (N379, N382, N385, TG6-28A, TG6-28B) encircles the urethra encircles urethra, reaches lateral surface of prostate and inferior bladder compresses urethra deep branch of perineal nerve from pudendal nerve internal pudendal a. skeletal muscle (Greek, sphincter = that which binds tight)
superficial transverse perineus medial surface of the ischial ramus contralateral muscle and the perineal body/central tendinous point fixes and stabilizes perineal body/central tendinous point deep branch of perineal nerve from pudendal nerve perineal a. superficial and deep transverse perineus muscles are separated by the perineal membrane
deep transverse perineus medial surface of the ischial ramus contralateral muscle and perineal body/central tendinous point fixes and stabilizes the perineal body/central tendinous point deep branch of perineal nerve from pudendal nerve internal pudendal a. superficial and deep transverse perineus muscles are separated by the perineal membrane

9. Trace the nerve and blood supply to the external genital organs. (W&B 524-525, N 404, 405, 411, 413, TG 6-29, 6-30A, 6-30B)

The nerve supply to the external genital organs is via the pudendal nerve, which gives off the dorsal clitoral or penile nerve, and also gives off the perineal nerve, which in turn gives off posterior labial or posterior scrotal nerves and the deep perineal nerve supplying all of the muscles of the urogenital triangle.

The internal pudendal artery gives off the dorsal artery of the clitoris or penis and the deep artery of the clitoris or penis as terminal branches. It also gives off an artery to the bulb of the vestibule (in females) or an artery to the bulb of the penis (in males). The perineal artery gives off a posterior labial or posterior scrotal artery.

10.Trace the lymphatic drainage of the perineum. (N 406, 407, 408A, 408B, TG 6-33, 6-34)
11. Trace the continuity of the abdominal peritoneum with that of the pelvic cavity. (W&B 533-534, N 360, 361, 362, 363, 371, TG 6-07A, 6-07B, 6-08A, 6-08B, 6-11, 6-13)

The peritoneum continues from the abdominal cavity into the pelvic cavity, but does not entirely invest the pelvic viscera. In the female, the peritoneum:

12. Describe the relationships of the bladder to other pelvic organs. (W&B 533-534, N 360, 361, 362, 366, 402, 403, 406, 407, 408, 410, TG 6-07A, 6-07B, 6-08A, 6-08B)

The bladder lies in the anterior half of the pelvis, bounded anteriorly and laterally by the pubic symphysis. Posterior to it we have:

Inferior to the bladder we find the pelvic diaphragm (in females) or the prostate gland (in males).

13. Identify the testis, its coverings, and tubules, and account for the difference in location between gonads in the two sexes. (W&B 431-433, 544-545, N 387, 390, TG 5-10, 6-31, 6-32)

The testes are covered by a tough, fibrous coat called the tunica albuginea testis. Superficial to that they are invested by two layers of tunica vaginalis testis, much like the pleura or peritoneum. (This structure is actually derived from the processus vaginalis of the peritoneum.) The visceral layer of the tunica vaginalis testis almost completely covers each, only being absent where the testis attaches to the epididymis. The parietal layer of the tunica vaginalis testis is more extensive yet, extending for a short distance along the spermatic cord. (Latin, tunica albuginea = white membrane, covering)

The gonads have a similar path of development in both sexes, up to a point. That point is when the ovaries try to start descending and find that the uterus is in the way. So, they stay where they are.

14. Trace the entire course of the ductus deferens from the epididymis to its ampulla; note its relationship to the ureter. (W&B 544, N 390, TG 6-32)

The epidiymis is a coil of tubes that lies on the posterior aspect of the testis. (The total length of each tube, if uncoiled, is 15-20 feet.) It is divided into three parts: (Greek, epi = upon, didymos = testicle, twin)

The ductus deferens passes superiorly to enter the inguinal canal through the superficial inguinal ring. It then passes superolaterally within the inguinal canal to enter the abdominal cavity through the deep inguinal ring. Turning medially and lying retroperitoneally, ductus passes over the external iliac vessels and descends into the pelvis and onto the superoposterior surface of the urinary bladder. Ductus crosses the ureter superiorly as the latter enters the posterior wall of the bladder. As the ductus approaches the midline, it turns inferiorly, nearly touching the contralateral ductus, and becomes ampullated, so that on the posterior surface of the bladder, both ampullae of the ductuli deferentes lie between the paired seminal vesicles. The ducts of both pairs of structures enter the posterior of the prostate to unite and form the ejaculatory duct on either side.

15. Identify the seminal vesicle and demonstrate the formation and course of the ejaculatory duct. (W&B 545-546, N 361A, 361B, 384A, 384B, TG 6-10)

The seminal vesicles lie lateral to the ampulla of the ductus deferens on the posterior side of the bladder. Their ducts join the ductus deferens to form the ejaculatory ducts. They are similar in structure to the ampulla of the ductus.

16. Identify the prostate gland and describe the special features of the prostatic urethral wall. (W&B 546-547, N 361, 384A, 384B, TG 6-10)

The prostate gland sits under the bladder, with the ampulla of the rectum posterior to it. (The rectovesical septum is between the two.) The base of the gland, which is the TOP, is continuous with the bladder wall. The ejaculatory ducts enter the prostate posterosuperiorly and run to the prostatic urethra.

The prostatic urethra is three to four centimeters long. The urethral crest is a ridge within it, and the prostatic sinuses are valleys on either side of the crest. The little ducts of the prostate gland empty into these sinuses.

The seminal colliculus is a rounded eminence in the middle of the prostatic urethra. A small slit in this structure leads to a very small blind pouch in the prostate. This pouch is the prostatic utricle (or "vagina masculina"), the male homologue of the uterus and vagina, i.e. the remnant of the Mullerian duct system. Near the mouth of the prostatic utricle, the two ejaculatory ducts empty into the prostatic urethra. (Latin, utriculus = little leather bag)

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Pelvis - The Muscles and Fasciž of the Pelvis - Female Organs of Reproduction 1, 2, 3, 4, 5 - Male Organs of Reproduction 1, 2, 3, 4, 5, 6 - Surface Anatomy of the Perineum - Surface Markings of the Perineum

Questions and Answers:

1a. Note the difference between male and female in the subpubic angle, the angle formed by the subpubic arch. What are other sex differences in the pelvic skeleton? (W&B 571-573, N 354, TG 6-05A, 6-05B, 6-05CD, 6-05EF)

Structure/Section Female Male
pelvic inlet oval and rounded heart-shaped
pelvic outlet large small
pubic arch and subpubic angle wide narrow
iliac wings flared less flared
2a. Define the ampulla of the ductus deferens. Is it covered by peritoneum? (N 361A, 361B, 384A, 384B, TG 6-14)

The ductus deferens is covered by peritoneum, but its ampulla is not. The upper end of the seminal vesicle may contact peritoneum, otherwise it is inferior to the peritoneum lining the rectovesical pouch.

3a. What is the rectovesical pouch? (N 361A, 361B, TG 6-08)

The rectovesical pouch is the reflection of peritoneum between the rectum and the bladder. This of course only occurs in males.

4a. Where does the transition of the epididymis to the ductus deferens occur? (N 390, TG 6-32)

It occurs at the tail of the epididymis on the posteroinferior aspect of the testis.

5a. Do you find muscular (deep) branches of the perineal nerves? (N 411, 413, TG 6-30A, 6-30B)
The deep perineal nerve innervates all of the muscles of the urogenital triangle via slender branches that may be difficult to locate.
6a. What is the source of the deep (central) artery of the clitoris/penis? (N 404, 405, 6-29A, 6-29B)
This artery is a branch of the internal pudendal artery.
7a. What is the source and drainage of the deep dorsal vein of the clitoris/penis and the dorsal veins and arteries of the clitoris/penis? (N 265, 383, 359, 404, 405, 381, TG 5-34, 6-10, 6-23, 6-27, 6-29)

The deep dorsal veins drain into the vesical venous plexus. The "normal" dorsal veins drain into the superficial external pudendal vein. The dorsal arteries come from the internal pudendal arteries.

8a. What is the function of the perineal membrane? (N 404, 405, 411, 413, TG 6-27A, 6-27B, 6-28A, 6-28B)
This membrane covers the anterior part of pelvic outlet. It aids in support of the pelvic viscera and as an attachment for perineal structures. It is pierced by the arteries of the erectile bodies and the dorsal arteries and nerves of the clitoris or penis.
9a. What gland is embedded in the sphincter urethrae muscle in males? (N 385A, 384B, 379A, 379B)
In males, the bulbourethral glands (Cowper's glands) are embedded in the external urethral sphincter muscle. In females, the greater vestibular gland is the homologous structure, but it is not associated with the sphincter urethrae muscle. (The greater vestibular glands lie posterior to the vestibular bulb, under the cover of the bulbospongiosus muscle.)