THE MALE and FEMALE PERINEUM: UROGENITAL TRIANGLE (Grant's Dissector [16Th Ed.] Pp
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THE MALE AND FEMALE PERINEUM: UROGENITAL TRIANGLE (Grant's Dissector [16th Ed.] pp. 148-153 [Male]; 165-170 [Female])
TODAY’S GOALS: 1. Identify components of the external genitalia in males and females. 2. Identify the location and contents of the superficial perineal space in males and females. 3. Identify the location and describe the contents of the deep perineal space in males and females.
DISSECTION NOTES: Male External Genitalia and Perineum I. Scrotum, Spermatic Cord and Testis (Dissector pp. 146-148). [If you have a female cadaver, see Dissector pp. 165-167 for a short description of the round ligament of the uterus exiting the superficial inguinal ring to the superior part of the labium majus]. Be aware that the scrotum, like the labium majus in the female, developed as an outpouching of the anterior abdominal wall. Near the superficial inguinal ring identify the spermatic cord. Insert a finger between the cord and the overlying skin and superficial fascia and work to separate these tissues into the scrotum. Using a scissors, make an anterior incision along this path through the skin and superficial (dartos) fascia into the scrotum. Follow the spermatic cord into the scrotum and mobilize the testis by transecting the scrotal ligament. The scrotal ligament (a remnant of the gubernaculum testis) “attaches/keeps in place” the inferior pole of the testis within the scrotal sac. Observe the scrotal septum which divides the scrotum into two compartments.
A. Contents and Fascial Coverings of the Spermatic Cord 1. Contents (Dissector Fig. 5.8, p. 147): • Ductus (vas) deferens and artery of the ductus deferens – palpate this hard, cord-like structure in the posterior aspect of the spermatic cord. (See Clinical Correlation Vasectomy in Dissector p. 147) • Testicular artery and pampiform plexus of veins (the latter consolidate into the testicular vein) • Lymph vessels and autonomic nerve fibers 2. Fascial coverings (Dissector Fig. 5.7, p. 146): With delicate dissection, attempt to identify these layers from superficial to deep. • External spermatic fascia – derived from the external oblique aponeurosis • Cremasteric muscle and fascia – derived from the internal oblique muscle; contains the genital branch of the genitofemoral nerve, which supplies the cremasteric muscle • Internal spermatic fascia – derived from the transversalis fascia. Deep to this fascial covering are the contents of the spermatic cord listed above
B. Testis 1. Coverings – from external to internal (Dissector Fig. 5.9, p. 148): Proceed by making a longitudinal incision with a sharp scalpel along the anterior border of the testis from its superior pole (location of the head of the epididymis) to the inferior pole (location of the tail of the epididymis) [the body of the epididymis is that segment located between these two poles] and open the testis up like a book. • Tunica vaginalis – a serosal sac derived from the processus vaginalis during descent of the gonad. Consists of two layers: i. Outer parietal layer ii. Inner visceral layer – with a small amount of serous fluid in the space between these two layers. During its descent, the visceral layer becomes applied to the medial, anterior, and lateral (but not the posterior) surfaces of the testis. • Tunica albuginea – a thick fibrous capsule of the testis to which the visceral layer of the tunica vaginalis is tightly attached. From its internal surface, observe delicate connective tissue septae project internally to divide the testis into lobules. 2. Duct system (structures involved in the transport of spermatozoa from the testis to the ductus deferens) • Seminiferous tubules – very fine, tightly coiled structures that fill each lobule. Each testis has about 250-1000 seminiferous tubules and each is about 30-70 cm in length. These converge on the rete testis (a network of anastomotic channels) in the mediastinal area on the posterior surface of the testis • Efferent ductules – about 10-20 efferent ductules arise from the network of channels in the rete testis and connect the rete to the head of the epididymal duct • Epididymis or epididymal duct – a single channel that consists of 3 segments: head, body, and tail • Ductus (vas) deferens – near the inferior pole of the testis, the tail of the epididymis makes a sharp turn and ascends as the ductus deferens within the spermatic cord. It passes through the superficial and deep rings enroute to the prostate gland.
Because the testis arises developmentally along the posterior abdominal wall, its lymphatic drainage is into lumbar and preaortic lymph nodes, whereas lymphatics from the scrotum drain into superficial inguinal lymph nodes. (See Clinical Correlation Lymphatic Drainage of the Testis in Dissector, p. 148)
II. Perineum The perineum is the diamond-shaped area between the upper thighs and below the inferior pelvic aperture and pelvic diaphragm. It is divided anatomically into 2 triangles: the (A) anal triangle (covered in Lab Anal Triangle) and the (B) urogenital (UG) triangle (Dissector p. 142, Fig. 5.2). The anal triangle is bounded by the tip of the coccyx, sacrotuberous ligaments, and a line connecting the right and left ischial tuberosities. It contains the anal canal, which pierced the levator ani muscle portion of the pelvic diaphragm. The urogenital triangle is bounded by the ischiopubic rami to the inferior surface of the pubic symphysis and a line connecting the right and left ischial tuberosities. This triangular space contains the urogenital (UG) diaphragm that transmits the urethra (in male) and urethra and vagina (in female).
A. Urogenital Triangle (Male) With the cadaver in a supine position and the thighs maximally abducted, make a midline incision beginning posterior to the shaft of the penis (Dissector p. 149, Fig. 5.10). Split the scrotum into right and left halves and continue the incision to the anal canal. Reflect the skin flaps laterally and try to discern two layers of superficial fascia, i.e., superficial fatty layer and a membranous layer (=Colles' fascia or superficial perineal fascia). This fascia is continuous with Scarpa's fascia of the lower anterior abdominal wall, the superficial penile fascia or dartos fascia of the penis, and the dartos fascia of the scrotum. The superficial perineal fascia is firmly attached to the right and left ischiopubic rami and to the posterior edge of the UG diaphragm (see Dissector p. 149, Fig. 5.11 and Clinical Correlation – Superficial perineal pouch on p. 149). • Superficial Perineal Space/Pouch Break through the superficial perineal fascia. Deep to this fascia is the superficial perineal space that contains erectile tissues of the penis and their associated musculature. Three pairs of skeletal muscle are located here (Dissector p. 150, Fig. 5.12): . Superficial transverse perineal muscles – slender; attach from each ischial tuberosity laterally and medially to the perineal body, a midline fibromuscular node between the scrotum and anus . Ischiocavernosus – arises from each ischiopubic ramus and covers the crus of the corpus cavernosum . Bulbospongiosus – covers the bulb of the penis and proximal portion of the corpus spongiosum In the triangular space between these muscles, identify the perineal membrane or inferior fascia of the UG diaphragm.
Attempt to find the superficial branch of the perineal nerve and artery whose branches supply the structures in the superficial perineal space.
• Penis (fascia, vessels, and nerves; Dissector p. 151, Fig. 5.13 and p. 152 Fig. 5.14) . Skin – remove skin along the dorsal surface from the glans to the shaft of the penis . Superficial penile fascia or dartos fascia of the penis – contains superficial dorsal vessels . Deep penile fascia (=Buck's fascia) – a thick investment of connective tissue that surrounds the erectile bodies (corpus cavernosum and corpus spongiosum). Incise this fascia on the dorsal surface from the glans to the symphysis pubis and identify: • Deep dorsal vein (unpaired, midline position) – passes through a gap at the inferior surface of the symphysis to communicate with the prostatic venous plexus • Dorsal arteries (paired) – terminal branches of the internal pudendal aa • Dorsal nerves (paired) – terminal branches of the pudendal nn . Glans – expanded distal end of the corpus spongiosum and contains the spongy or penile urethra and its external urethral orifice. . Identify the erectile bodies of tissues in a transverse section through the body of the penis (see Dissector p. 151, Fig 5.13). Make a transverse cut through the ventral surface of the penis about midway down its length. Extend the cut through the corpus spongiosum and most of the corpora cavernosae, but not all the way. Allow the remaining tissue to serve as a hinge to keep the penis otherwise intact. Examine the cut surface and observe the following: . Corpus cavernosum – a pair of erectile bodies formed by fusion of the crura of the penis. Identify the deep dorsal artery near the center of each erectile body. Surrounding the erectile tissue is a thickened wall called the tunica albuginea. . Corpus spongiosum – a single mass of erectile tissue on the ventral surface of the penis which surrounds and contains the spongy or penile urethra. It begins at the bulb of the penis and terminates in an expansion called the glans penis. Similarly, tunica albuginea also encircles this erectile tissue. . For a view of the relationship of these structures in a sagittal view, see Fig. 5.15 on p. 152 of the Dissector.
• Deep Perineal Space/Pouch (Dissector p. 153, Fig. 5.16) The space bounded by the inferior and superior fasciae of the UG diaphragm containing the musculature (skeletal) of this diaphragm, vessels and nerves, and the bulbourethral (Cowper’s glands). Do not attempt to find these structures. Contents of this space: . The UG diaphragm – is a skeletal muscle structure composed of: o Deep transverse perineal mm (paired) – attach to each ischiopubic ramus and to a midline raphe o Sphincter urethrae or external urethral sphincter – skeletal muscle that surrounds the membranous portion of the urethra (shortest portion of the urethra) . Branches of the internal pudendal artery (artery of the bulb of the penis, dorsal artery, deep dorsal artery) and of the pudendal nerve . Bulbourethral glands (Cowper's glands) – paired glands embedded within the deep pouch. Single ducts leave each gland and pass through the perineal membrane to empty into the proximal end of the spongy urethra.
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B. Urogenital Triangle (Female) (Dissector pp. 165,166, Figs. 5.26, 27) • External genitalia = vulva: . Mons pubis . Labia majora and minora . Vestibule of vagina (space between labia minora) . Clitoris - glans and its prepuce . Vaginal orifice . External urethral orifice With the cadaver in a supine position and the thighs maximally abducted, make a transverse incision between the right and left ischial tuberosities and that passes between the vagina and anus (Dissector p. 167, Fig. 5.27). From this horizontal incision, make a midline vertical incision to the symphysis pubis encircling the labia majora. Reflect the skin laterally and remove it. Note the fat of the labia majora and its continuity with fat from the lower anterior abdominal wall. Remove this fatty tissue.
Make a vertical incision along the lateral surface of a labia minora (it does not contain fat). In this process you will enter the superficial perineal space. Remove the remaining superficial perineal fascia laterally to the ischiopubic rami and identify contents of this space: • Superficial Perineal Space/Pouch (Dissector p. 168, Figs. 5.29 and 5.30) Contents: . Bulbospongiosus muscle – located along the lateral margin of the labia minora and covers the bulb of the vestibule (erectile tissue) and the greater vestibular glands = Bartholin's glands (located immediately posterior to each bulb of the vestibule). You will need to remove some of the muscle in order to see these structures. . Superficial transverse perineal muscles – (slender [may be difficult to find]; attach from an ischial tuberosity to the perineal body = midline fibromuscular node between the vagina and anus) . Ischiocavernosus muscle – located lateral to the bulbospongiosus and arises from an ischiopubic ramus and covers the crus of the clitoris In the triangular space between these muscles, identify the perineal membrane or inferior fascia of the UG diaphragm.
Attempt to find the superficial branch of the perineal nerve and artery whose branches supply the structures in the superficial perineal space.
The body of the clitoris is formed by the union of the two corpora cavernosa and the glans clitoris caps the corpora cavernosa.
• Deep Perineal Space (Dissector p. 169, Fig. 5.31) The space bounded by the inferior and superior fasciae of the UG diaphragm containing the musculature (skeletal) of this diaphragm, urethra, part of the vagina, vessels and nerves. Do not attempt to find these structures. Contents of this space include: . The UG diaphragm – is a skeletal muscle structure composed of: o Deep transverse perineal mm (paired) – attach to each ischiopubic ramus and to the perineal body o Sphincter urethrae or external urethral sphincter – skeletal muscle that surrounds the membranous portion of the urethra (shortest portion of the urethra) o Compressor urethrae o Urethrovaginalis . Branches of the internal pudendal artery (dorsal artery of the clitoris) and of the pudendal nerve (dorsal nerve of the clitoris).
PEER TEACHING GUIDE: 1. Demonstration of the components of the external genitalia in males and females. 2. Demonstration of the contents of the superficial perineal pouch in males and females, including location of erectile tissues and associated musculature. 3. Demonstration of the location and description of the deep perineal pouch and its contents.