Pelvis Lab 7A

Lab 7A: Urogenital Triangle

Lab Overview

Identify the erectile tissues and muscles that are part of the external genitalia.
Be sure to spend time with a pelvis of the opposite sex (of your cadaver).

Short List of Structures - 7A

Corpus spongiosum erectile tissue
Junction of the two corpora cavernosa
Ischiocavernosus m.
Bulbospongiosus m.
Bulb of the vestibule (female) or bulb of the penis (male)

Overview and Homologs of the Urogenital Triangle

Male Urogenital Triangle

Identify the following structures:

Shaft of the penis — the body of the penis
Glans penis — the head or tip of the penis
Penile raphe — located on the ventral surface of the penis

To remove the skin and fat from both sides of the UG triangle and scrotum, follow these instructions. Note that UG triangle is shown intact in Figure 5.2, but you will be working with a split pelvis to make access easier.

Use forceps and your fingers to separate both testicles from the scrotum
With a scalpel or scissors, cut off the scrotum where it is attached posteriorly and laterally over the UG triangle and from the base of the penis, but do not cut the penis

Shaft of the Penis

Superficial penile fascia — continuous with Scarpa's and Dartos fasciae; devoid of fat tissue
Superficial dorsal v.—drains to the external pudendal v.
Deep penile fascia — also called Buck's fascia
Tunica albuginea — connective tissue sheath surrounding the erectile tissues; forms the septum penis, which separates the corpora cavernosa
Corpora cavernosa (two) — paired dorsal erectile tissue bodies
Corpus spongiosum — ventral erectile tissue that contains the spongy urethra

Superficial Perineal Space — Contents

Use forceps to reveal and identify the following three muscles of the superficial perineal space:
- Ischiocavernosus mm. — paired muscles that cover each crus of the corpora cavernosa

Follow the paired corpora cavernosa laterally and posteriorly proximally to their respective attachment on each ischiopubic (conjoint) ramus. These fixed (nonpendulous) parts of the penis are called crura (legs); both crura are covered superficially (inferiorly) by an ischiocavernosus m. You will need to dissect laterally to see the extent of the erectile tissue, this means you will dissect deep if you are viewing the cut edge of the sagittally sectioned pelvis.

Bulbospongiosus m. — covers the midline corpus spongiosum that makes up the Bulb of the penis
Superficial transverse perineal m. — attaches laterally to the ischial tuberosities, and medially into the perineal body.

HELPFUL HINTS

The ischiocavernosus mm. and bulbospongiosus m. are very thin. The best way to demonstrate them is the peel away any remaining skin and fascia from the base/bulb on the ventral side of the penis. Once here, you can move laterally and slowly dissect any fascia and fat away until you get to the bases of the crura of the penis. If you dissect very patiently, you can demonstrate the delicate fibers of these mm.

Female Urogenital Triangle

External Genitalia — Perineum

Identify the following:

Mons pubis — skin and adipose tissue superficial to the pubic symphysis; point of attachment for the round ligament of the uterus
Labia majora — two large folds of skin filled with adipose tissue; they are joined anteriorly by the anterior labial commissure; pubic hair lines this region of the perineum
Labia minora — two thin delicate folds of adipose-free, hairless skin that lie between the labia majora and enclose the vestibule of the vagina; lie on each side of the opening of the urethra and vagina
Vestibule — space between the labia minora
Clitoris — located between the anterior ends of the labia minora; composed of erectile tissue, and capable of erection
External urethral orifice — opening for the urethra; anterior to the vaginal orifice
Vaginal orifice — opening for the vagina; positioned between the external urethral orifice and the anus
Anus — opening for the rectum; posterior to the vaginal orifice

Dissection of the Urogenital Triangle

The UG triangle is shown intact in Figure 5.7, but you will be working with a split pelvis to make access easier
Make the following incisions, using a scalpel:
Cut between the labia majora and labia minora
Remove the skin overlying the labia majora and minora to remove skin and fat from both sides of the UG triangle
Reflect the skin and fat to reveal the underlying muscles in the superficial perineal space, you can choose to remove the skin (following the dashed lines in the image to the right) or you can leave the skin attached.
You will need to dissect laterally to see the extent of the erectile tissue, this means you will dissect deep if you are viewing the cut edge of the sagittally sectioned pelvis.

Observe the following structures of the clitoris.

Tunica albuginea — white, connective tissue sheath surrounding the erectile tissues; forms the septum clitoris, which separates the corpora cavernosa tissue
Corpora cavernosa (two) — paired erectile tissue bodies form the crura (legs; singular crus) of the clitoris running posterolaterally along the inferior ramus of the pubis and ramus of the ischium (on both sides)
Superficial clitoral fascia — continuous with Scarpa's fascia
Bulb of the vestibule (two) — paired corpus spongiosum erectile tissue bodies on either side of the vestibule (surrounding the vaginal and urethral openings).

HELPFUL HINTS

You will not be able to do a cross-section of the shaft of the clitoris because a mid-sagittal section was previously performed. This figure is useful, however, to help you understand the arrangement of the erectile tissues.

Superficial Perineal Space — Contents

Use forceps to reveal and identify the following muscles of the superficial perineal space:

Ischiocavernosus mm. — paired muscles that cover each crus of the corpora cavernosa.

Follow the paired corpora cavernosa laterally and posteriorly to their respective attachment on each ischiopubic (conjoint) ramus. These fixed (nonpendulous) parts of the clitoris are called crura (legs); both crura are covered superficially by a thin muscle called the ischiocavernosus m.

Bulbospongiosus m. — covers the Bulb of the vestibule.

Clean the area between the crura and vaginal orifice to locate the bulbospongiosus m. fibers on the lateral surface of the labia minora. Follow the bulbospongiosus m. posteriorly to its attachment to the perineal body and the inferior fascia of the UG diaphragm

- - The perineal body is a midline thickening where the bulbospongiosus, superficial transverse perineal, deep transverse perineal, and external anal sphincter mm. converge
Superficial transverse perineal m. — attaches laterally to the ischial tuberosities, and medially into the perineal body.

HELPFUL HINTS

The erectile tissue and their surrounding muscles degenerate with age and may be difficult to find. Be patient, the muscles are very thin, it’s easy to dissect right through them.

Relationship of the erectile tissues of the clitoris to the bones of the pelvis. Note that the paired crura (legs) of the clitoris run posterolaterally along the inferior ramus of the pubis and ramus of the ischium (on both sides)

Clitoral morphology with different levels of testosterone. The three columns show the same anatomy with different skin tones.

Clinical Correlation: Diversity in external genitalia

In human cultures, external (and internal) genitalia are a socially, scientifically, and personally loaded topic.
However, as we have seen in our development lectures, all fetuses start out with the same sets of organs and it is the relative hormonal expression during development that influences shape and function.
External genitalia come in all shapes and sizes. No one morphology is “right” if the morphology is not causing mental or physical harm to the patient.
Many patients will come in with questions about what they think their body should be versus the reality, but may be too embarrassed to ask due to social taboos.
Other people may be diagnosed with disorders such as body dysmorphia or gender dysphoria, but it is important not to assume this is the case without a complete history and consultation with other experts.
Still others may have lost part of their external genitalia from an accident or infection and may feel shame.
There are many transgender patients who have been taking hormones for a number of years and they may be proud of their anatomy. The image to the left is a visual depiction of how androgenic hormone replacement therapy can change external genetalia.

In conclusion: human genitalia are diverse! Embrace the diversity.

Genetalia Homologues

Homologues of External Genetalia

Homologues of Internal Genetalia

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