THE PELVIS AND PERINEUM – PROSECTION LABORATORY GUIDE
The pelvis is the area of transition between the trunk and the lower limbs. The bony pelvis serves as the foundation for the pelvic region and provides strong support for the vertebral column upon the lower limbs. The pelvic cavity is continuous with the abdominal cavity, the transition occurring at the plane of the pelvic inlet (Figure 5.1). The pelvic cavity contains the rectum, the urinary bladder, and the internal genitalia.
The perineum is the region of the trunk that is located between the thighs and is located inferior to the pelvic cavity. The pelvic diaphragm separates the pelvic cavity from the perineum (Figure 5.1). The perineum contains the anal canal, a portion of the urethra, and the external genitalia (penis and scrotum in the male, vulva in the female).
This guide begins with a review of the surface anatomy of the perineum that you first encountered during the Osteology/Radiology/Surface Anatomy component of Clinical Skills 101. This is followed by a study of the osteology of the pelvis. Then the musculoskeletal boundaries and compartments of the pelvic cavity and the perineum are described. Subsequent labs will consider the pelvic viscera, the pelvic neurovasculature, and a detailed study of the male perineum. Details of the female perineum and the pelvic diaphragm that are relevant to your third year Obstetrics/Gynecology Clerkship will be considered during intersessions preceding the clerkships.
All of the laboratory exercises make use of prosected specimens. Many of these will be pelves that have been sagittally cut. These will be found in plastic bags at the feet of the cadavers on the dissecting tables. Above each table will be signage indicating what specimen is located on that table. Dissecting teams will not have a table assignment for this reproduction block. You should work as a dissecting team (A or B) and move around the lab studying the various prosected specimens. It will be extremely unusual for you to find all the structures (e.g., the vasculature) in one specimen.
Surface Anatomy and Osteology
You have previously studied the surface anatomy of the external genitalia during the Clinical Skills 101 course. This is a good opportunity to review this anatomy (we reserve the right to test you again on this material in the context of this block).
Use the intact cadavers in the laboratory for a review of the surface anatomy of the male and female perineum.
Review the surface anatomy of the female perineum.
1. Place the cadaver in a supine position. Stretch the thighs widely apart using the hardware available in the lab (ask your instructor for details) or wooden blocks.
2. Identify the vulva and identify the following structures (Figure 5.25):
Review the surface anatomy of the male perineum.
3. Place the cadaver in a supine position. Stretch the thighs widely apart using the hardware available in the lab (ask your instructor for details) or wooden blocks.
4. Identify the following structures (Figure):
5. Refer to an articulated bony pelvis and a skeleton. The pelvis (L. pelvis, basin) is formed by two hip bones (coxal bones, ossa coxae) joined posteriorly by the sacrum (Figure 5.2). Each hip bone is formed by three fused bones: pubis, ischium, and the ilium. These three bones are fused at the acetabulum. The coccyx is attached to the sacrum. As you study isolated bones such as the hip bone, compare its features with the articulated bony pelvis and the skeleton.
6. On the hip bone (Figure 5.2), identify the:
7. On the sacrum, identify the:
8. Identify the coccyx at the caudal end of the sacrum.
9. Examine the ischium. Note that the ischial spine divides the posterior margin of the body of the ischium into two large notches – the greater sciatic notch (located superior to the ischial spine) and the lesser sciatic notch (inferior to the ischial spine).
10. Using an atlas illustration, study the joint between the sacrum and ilium. The sacroiliac articulation is a synovial joint between the auricular surfaces of the sacrum and the ilium. The sacroiliac articulation is strengthened by an anterior sacroiliac ligament and a posterior sacroiliac ligament (Figure 5.2). The articulation between the ilium and the L5 vertebra is strengthened by the iliolumbar ligament. Do not attempt to find these ligaments on the skeleton or cadaver.
11. The hip bone and sacrum are connected by strong ligaments (Figure 5.2). On a model with pelvic ligaments, identify the sacrotuberous ligament, a ligament extending from the inferolateral angle of the sacrum (“sacro-“) to the ischial tuberosity (“-tuberous”).
12. Identify the sacrospinous ligament, a ligament extending from the inferolateral angle of the sacrum (“sacro-“) to the ischial spine (“-spinous”).
13. Note that the sacrotuberous and sacrospinous ligaments convert the greater and lesser sciatic notches into greater and lesser sciatic foramina, respectively. The greater sciatic foramen is located superior to the sacrospinous ligament. The lesser sciatic foramen is located inferior to the sacrospinous ligament, between it and the sacrotuberous ligament.
14. Identify the pelvic inlet (superior pelvic aperture), a large communication between the greater pelvis (also called the false pelvis or pelvis major) and the lesser pelvis (also called the true pelvis, pelvis minor, or the “obstetric pelvis”) (Figure 5.1). The greater pelvis is situated superior to the pelvic inlet and is bounded bilaterally by the right and left alae of the ilium, the wing-like upward projections of the right and left ilia. The concave anterior surface of the ala of each ilium is called the iliac fossa. The cavity of the greater pelvis is considered to be part of the abdominal cavity.
15. The bony ridge forming the border around the pelvic inlet is called the pelvic brim (Figure 5.2, lower right panel). From anterior to posterior, identify the structures that form the pelvic brim:
16. The lesser pelvis is located inferior to the pelvic inlet and extends inferiorly to the urogenital and pelvic diaphragms, which close the pelvic outlet (described later).
MUSCULOSKELETAL BOUNDARIES OF THE LESSER PELVIS
1. Using an articulated bony pelvis with the sacrotuberous and sacrospinous ligaments, examine the walls of the lesser pelvis. The posterolateral wall comprises the pelvic (anterior) surface of the sacrum and the muscular contents of the greater sciatic foramen, i.e., the piriformis muscle (Figure 3.11). Place one end of a wet paper towel on the lateral border of the sacrum, passing the other end through the greater sciatic foramen. This towel represents the piriformis muscle, with its tendon passing out through the greater sciatic foramen.
2. The anterolateral wall of the lesser pelvis comprises (on each side) the body of the pubic bone, the obturator foramen and the bones forming its margin, the body of the ischium, and the muscular contents of the lesser sciatic foramen, i.e., the obturator internus muscle (Figure 3.11), which also covers over the obturator foramen from the inside. Pass one hand through the pelvic inlet and cover the obturator foramen from the inside. This is where you will place one end of a second wet paper towel, replacing your hand with it. Pass the other end through the lesser sciatic foramen. This towel represents the obturator internus muscle, with its tendon passing out through the lesser sciatic foramen.
3. Identify the pelvic outlet (inferior pelvic aperture), which is the inferior opening not filled in with paper towel. The pelvic outlet is bounded on each side by the:
4. Examine the superior border of the ala of the ilium, called the iliac crest. The iliac crest extends from the anterior superior iliac spine (ASIS) anteriorly to the posterior superior iliac spine (PSIS) posteriorly. Identify these features on the articulated bony pelvis.
5. In the erect posture, i.e., the anatomical position, the anterior superior iliac spines and the superior end of the pubic symphysis lie in the same vertical plane. Hold the articulated bony pelvis in the anatomical position. Observe that, in this position, the plane of the pelvic inlet forms an angle of approximately 55° to the horizontal plane (See Figure).
6. While still holding the articulated bony pelvis in the anatomical position, observe that the posterolateral wall of the lesser pelvis, consisting of the pelvic surface of the sacrum, the greater sciatic foramina and the piriformis muscles, is well superior to the anterolateral wall, consisting of the pubic bones, a portion of the ischii, the obturator internus muscles and the lesser sciatic foramina. Because this is the orientation of the pelvis in the erect position, the anterolateral wall biomechanically constitutes a weight-bearing floor rather than a wall of the pelvic cavity.
7. Note that all structures that exit the lesser pelvis, which originate from the posterolateral wall (except for the obturator artery), exit the lesser pelvis through the greater sciatic foramen. These structures include the piriformis muscle and tendon, nerves derived from the lumbosacral plexus, and exiting arteries. In contrast, structures that exit the lesser pelvis, which originate from the anterolateral wall, exit the lesser pelvis through the lesser sciatic foramen (namely, the obturator internis tendon). The lesser sciatic foramen also serves as the doorway to the perineum. We will later encounter neurovascular structures that enter the perineum by passing in through the lesser sciatic foramen.
8. While using the articulated bony pelvis with the two towels in place as references, examine the pelvic cavity in a prosected cadaveric pelvis. Attempt to identify the obturator internus muscle in the cadaver. If identification of the obturator internis muscle is difficult, recall that the proximal attachment of the obturator internis muscle is the inner border of the obturator foramen. To locate the obturator foramen, identify the pubic symphysis (remember that the pelvis has been bisected in the midline) and the pubic crest. Follow the pubic crest laterally to find the superior pubic ramus, which is the superior margin of the obturator foramen. The muscle directly inferior and partially attached to the superior pubic ramus is the obturator internis muscle.
9. Attempt to identify the piriformis muscle in the cadaveric pelvis (Figure 3.11). If identification of the piriformis muscle is difficult, recall that the proximal attachment of the piriformis muscle is the lateral border of the sacrum. Look for the sectioned midline of the sacrum and trace the pelvic surface of the sacrum laterally to locate the piriformis muscle. An important relation of the piriformis muscle is the sacral plexus, a series of nerves (ventral rami of the sacral spinal nerves actually) that exit the sacrum via the anterior sacral foramina. The nerves of the sacral plexus pass inferolaterally over the anterior surface of the piriformis muscle toward the greater sciatic foramen. The sacral plexus will be examined in more detail later but make an initial attempt to identify these nerves now.
10. The remaining muscles in the cadaveric pelvis contribute to the pelvic floor (Figure 3.11). The pelvic floor consists of a series of muscles (see Diagram) that close the pelvic outlet, allowing portions of the urinary, genital and alimentary tracts to pass. The majority of the pelvic outlet is closed by the pelvic diaphragm, except for a small anterior hiatus that’s closed by the urogenital diaphragm (do not attempt to identify the urogenital diaphragm at this time).
[THE PELVIC DIAPHRAGM WILL BE STUDIED IN DETAIL DURING THE INSTERSESSIONS PRECEDING THE OBSTERICS / GYNECOLOGY CLERKSHIPS. RIGHT NOW IT IS SUFFICIENT FOR YOU TO UNDERSTND THAT THE PELVIC DIAPHRAGM CLOSES OFF THE MAJORITY OF THE PELVIC OUTLET AND SUPPORTS THE UTERUS AND THE RECTUM. IF THE PELVIC DIAPHRAGM BECOMES LAX, THESE VISCERAL STUCTURES CAN PROLAPSE.]
MUSCULOSKELETAL BOUNDARIES OF THE PERINEUM
The perineum is a diamond-shaped area between the thighs, which is divided for descriptive purposes into two triangles (Figure 5.3). The anal triangle is the posterior half of the diamond and contains the anus. The urogenital triangle is the anterior half of the diamond and contains the external urethral orifice and the external genitalia. Deep to the skin of the urogenital triangle are the superficial and deep pouches of the perineum. Deep to the skin of the anal triangle are a pair of ischioanal fossae, which are separated from the pelvic cavity by the pelvic diaphragm (see area labeled “perineum” in Figure 5.1).
1. Examine an articulated bony pelvis with sacrotuberous and sacrospinous ligaments. The perineum has 4 boundaries, defining a diamond-shaped region (Figure 5.3), consisting of:
a) a line from the inferior end of the pubic symphysis, along the left ischiopubic ramus to the left ischial tuberosity.
b) a line from the left ischial tuberosity, along the left sacrotuberous ligament to the inferolateral angle of the sacrum.
c), d) the corresponding lines on the right side of the pelvis.
2. Envision an imaginary transverse line between the ischial tuberosities. This line divides the perineum into a pair of two-dimensional surfaces, the urogenital (anterior) and anal (posterior) triangles.
[The anal triangle, the ischioanal fossae, and the pelvic diaphragm will be studied during laboratory exercises that are part of the intersessions preceding the Obstetrics / Gynecology Clerkships.]
3. Examine the sectioned midline of a bisected cadaveric pelvis. Deep to the skin of the urogenital triangle are the superficial and deep perineal pouches.
4. Identify the pubic symphysis. Within the horizontal plane, identify a thin line of muscle between the inferior end of the pubic symphysis and the anal canal. This is the urogenital diaphragm, which is the major structure within the deep perineal pouch (other structures embedded with the urogenital diaphragm will be described later). Consequently, it is important to understand that the deep perineal “pouch” is essentially filled with the urogenital diaphragm.
5. Superior to the urogenital diaphragm is the pelvic cavity.
6. While looking at the sectioned midline of a bisected cadaveric pelvis, look for a thin white sheet of fascia (a line in this sagittal section) on the inferior surface of the urogenital diaphragm. This is the inferior fascia of the urogenital diaphragm (also called the perineal membrane) and is the boundary between the superficial and deep perineal pouches. Thus, the deep perineal pouch is located superior to the perineal membrane.
7. Inferior to the perineal membrane is the superficial perineal pouch. Understand that the word “superficial” means closer to the skin surface whereas “deep” means farther from the skin surface. Thus, in this case, because the perineum is conceptually “upside-down”, it should not be counterintuitive that the superficial perineal pouch is inferior to the deep perineal pouch. The superficial boundary of the superficial perineal pouch is the skin of the urogenital triangle. Based on these landmarks, identify the approximate location of the superficial perineal pouch in the bisected cadaveric pelvis.
The male pelvic cavity contains the urinary bladder and male internal genitalia anteriorly, and the rectum posteriorly (Figure 5.17). The peritoneum will be studied in the male pelvic cavity. The cut surface of the sectioned pelvis will be studied. The ductus deferens will be traced from the anterior abdominal wall to the region between the urinary bladder and rectum. The seminal vesicles and prostate gland will be studied.
The female pelvic cavity contains the urinary bladder anteriorly, the female internal genitalia, and the rectum posteriorly (Figure 5.30). The term adnexa (L. adnexa, adjacent parts) refers to the ovaries, uterine tubes, and ligaments of the uterus. Removal of the uterus (hysterectomy), with or without the ovaries, is a common surgical procedure. If the uterus has been surgically removed from your cadaver, examine it in another cadaveric pelvis. The peritoneum will be studied in the female pelvic cavity. The cut surface of the sectioned pelvis will be studied. The uterus and vagina will be studied. The uterine tube will be traced from the uterus to the ovary. The ovary will be studied.
PERITONEUM [THE PERITONEUM OF THE MALE AND FEMALE PELVES SHOULD BE EXAMINED IN THE CADAVERS.]
The peritoneum is a serous membrane that lines the walls of the abdominopelvic cavity and covers the viscera. The pelvic viscera are retroperitoneal organs (more specifically, they are sometimes referred to by physicians as “infraperitoneal” or “subperitoneal”) in that the peritoneum drapes over the superior surfaces of these organs, partially covering them, rather than suspending them from the wall. As the peritoneum loops in and out of the spaces between the pelvic organs, pouches and fossae (sing. Fossa; L. for ditch/depression) are formed, representing gravitational minima where the accumulation of fluids and infections can occur.
IN THE CLINIC: Pelvic Peritoneum
As the urinary bladder fills, the peritoneal reflection is elevated above the level of the pubis and is raised from the anterior abdominal wall (Figure 5.17; Figure 5.30). A filled urinary bladder can be approached with a needle just superior to the pubis without entering the peritoneal cavity.
IN THE CLINIC: Lymphatic Drainage of the Labium Majus
Lymphatics from the labium majus drain to the superficial inguinal lymph nodes. Inflammation of the labium majus may cause tender, enlarged superficial inguinal lymph nodes.
Male Internal Genitalia
The male internal genitalia consist of the prostate, seminal vesicles, and the ductus deferens. To locate these structures in the male, we will begin with the external genitalia, identify the spongy urethra within the penis, and trace the urethra proximally to the prostate.
Study the cut surface of the sectioned specimen:
1. Begin in the superficial perineal pouch and identify the bulb of the penis (Figure 5.15). The bulb of the penis is the unpaired, midline portion of the root of the penis. The bulb of the penis is continuous with the ventral portion of the body of the penis, called the corpus spongiosum. The spongy urethra passes through both the bulb of the penis and the corpus spongiosum en route to the external urethral orifice. Trace the spongy urethra proximally to the deep perineal pouch.
2. Review the perineal membrane. It is located deep to the bulb of the penis and can be identified as a thin line at the deep edge of the bulb (Figure 5.15). Superior (deep) to the perineal membrane, in the deep perineal pouch, the external urethral sphincter muscle surrounds the membranous urethra (do not attempt to identify the external urethral sphincter). Trace the membranous urethra proximally to the pelvic cavity.
3. Observe the prostate (Figure 5.17). The apex of the prostate is directed inferiorly and the base of the prostate is located superiorly against the neck of the urinary bladder. On the sectioned pelvis, trace the path of a drop of urine from the urinary bladder to the external urethral orifice. Identify once again the three parts of the urethra: prostatic urethra, membranous urethra, and spongy urethra (Figure 5.15).
4. Find the ductus deferens where it enters the deep inguinal ring lateral to the inferior epigastric artery and vein (Figure 5.19).
5. Trace the ductus deferens from the deep inguinal ring toward the midline. Observe that the ductus deferens passes superior and then medial to the branches of the internal iliac artery. Note that the ductus deferens crosses superior to the ureter.
6. Trace the ductus deferens into the rectovesical septum, which is the endopelvic fascia between the rectum and the urinary bladder. Observe that the ductus deferens is in contact with the fundus (posterior surface) of the urinary bladder.
7. Identify the ampulla of the ductus deferens, which is the enlarged portion just before its termination (Figure 5.19).
8. Identify the seminal vesicle. The seminal vesicle is located lateral to the ampulla of the ductus deferens in the rectovesical septum.
9. Close to the prostate, the duct of the seminal vesicle joins the ductus deferens to form the ejaculatory duct. The ejaculatory duct is delicate and easily torn where it enters the prostate. The ejaculatory duct empties into the prostatic urethra on the seminal colliculus (Figure 5.18).
Female Internal Genitalia
URINARY BLADDER, RECTUM, AND ANAL CANAL
The urinary bladder is a reservoir for urine. When empty, it is located within the pelvic cavity. When filled, it extends into the abdominal cavity. The urinary bladder is a retroperitoneal organ that is surrounded by endopelvic fascia. Between the pubic symphysis and the urinary bladder there is a potential space called the retropubic space (also called the prevesical space or the Space of Retzius; Figure 5.17 and Figure 5.30). The retropubic space is filled with fat and loose connective tissue that accommodates the expansion of the urinary bladder. In the male, the puboprostatic ligament is a condensation of fascia that ties the prostate to the inner surface of the pubis. In the female, the pubovesical ligament is a condensation of fascia that ties the neck of the urinary bladder to the pubis across the retropubic space. The puboprostatic (in the male) or the pubovesical ligament (in the female) defines the inferior limit of the retropubic space (Figure 5.17 and Figure 5.30). The lower one-third of the rectum is surrounded by endopelvic fascia. The middle and upper thirds of the rectum are partially covered by endopelvic fascia and peritoneum (Figure 5.17 and Figure 5.30).
a. Apex – the pointed part directed toward the anterior abdominal wall. The apex of the urinary bladder can be identified by the attachment of the urachus.
b. Fundus – the inferior part of the posterior wall, also called the base of the urinary bladder. In the male, the fundus is related to the ductus deferens, seminal vesicles, and rectum. In the female, the fundus is related to the vagina and cervix.
c. Body – between the apex and the fundus.
d. Neck – where the urethra exits the urinary bladder. In the neck of the urinary bladder, the wall thickens to form the internal urethral sphincter, which is an involuntary muscle.
a. Superior – covered by peritoneum
b. Posterior – covered by peritoneum on its superior part and by endopelvic fascia on its inferior part
c. Inferolateral (2) – covered by endopelvic fascia
4. Identify the trigone on the inner surface of the fundus (Figure 5.18 and Figure 5.34). The angles of the trigone are the internal urethral orifice and the two orifices of the ureters. The internal urethral orifice is located at the most inferior point in the urinary bladder.
5. Observe that the mucous membrane over the trigone is smooth. The mucous membrane lining the other parts of the urinary bladder lies in folds when the urinary bladder is empty but will accommodate expansion.
6. Insert the tip of a probe into the orifice of the ureter and observe that the ureter passes through the muscular wall of the urinary bladder in an oblique direction. When the urinary bladder is full (distended), the pressure of the accumulated urine flattens the part of the ureter that is within the wall of the urinary bladder and prevents reflux of urine into the ureter.
IN THE CLINIC: Kidney Stones
Kidney stones pass through the ureter to the urinary bladder and they may become lodged in the ureter. The point where the ureter passes through the wall of the urinary bladder is a relatively narrow passage. If a kidney stone becomes lodged, severe colicky pain results. The pain stops suddenly once the stone passes into the bladder.
Rectum and Anal Canal
1. The rectum begins at the level of the third sacral vertebra. Observe the sectioned pelvis and note that the rectum follows the curvature of the sacrum.
2. Identify the ampulla of the rectum (Figure 5.35). At the ampulla, the rectum bends approximately 80° posteriorly (anorectal flexure) and is continuous with the anal canal. In the male, observe that the prostate and seminal vesicles are located close to the anterior wall of the rectum (Figure 5.17).
3. Examine the inner surface of the rectum. Note that the mucous membrane is smooth except for the presence of transverse rectal folds. There is usually one transverse rectal fold on the right side and two on the left side. The transverse rectal folds may be difficult to identify in some cadavers.
5. Examine the inner surface of the anal canal (Figure 5.35). The mucosal features of the anal canal may be difficult to identify in older individuals, but attempt to identify the following:
a. Anal columns – 5 to 10 longitudinal ridges of mucosa in the proximal part of the anal canal. The anal columns contain branches of the superior rectal artery and vein.
b. Anal valves – semilunar folds of mucosa that unite the distal ends of the anal columns. Between the anal valve and the wall of the anal canal is a small pocket called an anal sinus.
c. Pectinate line – the irregular line formed by all of the anal valves.
6. The anal sphincter muscles surround the anal canal. Identify the external anal sphincter muscle and the internal anal sphincter muscle in the sectioned specimen (Figure 5.35). The longitudinal muscle of the anal canal (i.e., the outer layer of the muscularis externa) separates the two sphincter muscles.
IN THE CLINIC: Rectal Examination
In the male, digital rectal examination is part of the physical examination. The size and consistency of the prostate gland can be assessed by palpation through the anterior wall of the rectum.
IN THE CLINIC: Hemorrhoids
In the anal columns, the superior rectal veins of the hepatic portal system anastomose with middle and inferior rectal veins of the inferior vena caval system. An abnormal increase in blood pressure in the hepatic portal system causes engorgement of the veins contained in the anal columns, resulting in internal hemorrhoids. Internal hemorrhoids are covered by mucous membrane and are relatively insensitive to painful stimuli because the mucous membrane is innervated by autonomic nerves.
External hemorrhoids are enlargements of the tributaries of the inferior rectal veins. External hemorrhoids are covered by skin and are very sensitive to painful stimuli because they are innervated by somatic nerves (inferior rectal nerves).
[The pelvic neurovasculature of the male will be emphasized during this laboratory exercise. The female pelvic neurovasculature will get additional emphasis during laboratory activities that will precede the Obsterics/Gynecology clerkship during the third year intersessions.]
The somatic plexuses of the pelvic cavity are the sacral plexus and coccygeal plexus. These plexuses are located between the pelvic viscera and the lateral pelvic wall within the endopelvic fascia. These somatic nerve plexuses are formed by contributions from ventral rami of spinal nerves L4 to S4. The primary visceral nerve plexus of the pelvic cavity is the inferior hypogastric plexus. It is formed by contributions from the hypogastric nerves, sympathetic trunks, and pelvic splanchnic nerves.
1. Identify the rectum and note its relationship to the anterior surface of the sacrum and coccyx.
2. Retract the rectum medially and identify the sacral plexus of nerves. The sacral plexus is closely related to the anterior surface of the piriformis muscle. Review the attachments and relations of the piriformis muscle. Verify the following (Figure 5.23 and Figure 5.37):
o The lumbosacral trunk (ventral rami of L4 and L5) joins the sacral plexus.
o The ventral rami of S2 and S3 emerge between the proximal attachments of the piriformis muscle.
o The sciatic nerve is formed by the ventral rami of spinal nerves L4 through S3. The sciatic nerve exits the pelvis by passing through the greater sciatic foramen, usually inferior to the piriformis muscle.
IN THE CLINIC: Pelvic Nerve Plexuses
The pelvic splanchnic nerves (parasympathetic outflow of S2, S3, and S4) are closely related to the lateral aspects of the rectum. These autonomic nerve plexuses can be injured during surgery, causing loss of bladder control and erectile dysfunction.
Anterior to the sacroiliac articulation, the common iliac artery divides to form the external and internal iliac arteries (Figure 5.22 and Figure 5.36). The external iliac artery distributes to the lower limb and the internal iliac artery distributes to the pelvis. The internal iliac artery has the most variable branching pattern of any artery, and it is worth noting at the outset that you must use the distribution of the branches (i.e., the structures they are supplying) to identify them, not their pattern of branching.
The internal iliac artery commonly divides into an anterior division and a posterior division. Branches arising from the anterior division are mainly visceral (branches to the urinary bladder, internal genitalia, external genitalia, rectum, and gluteal region). Branches arising from the posterior division are parietal (branches to the pelvic walls and gluteal region).
Ø Inferior vesical artery – courses toward the fundus of the urinary bladder to supply the urinary bladder, seminal vesicle, and prostate. The inferior vesical artery is a named branch only in the male; in the female it is an unnamed branch of the vaginal artery.
Ø Uterine artery – courses along the inferior attachment of the broad ligament. Trace it to the lateral aspect of the uterus and note that it passes superior to the ureter. The uterine artery divides into a large superior branch to the body and fundus of the uterus and a smaller branch to the cervix and vagina. Observe the close relationship of the lateral part of the vaginal fornix to the uterine artery. In a living person, the pulsations of the uterine artery may be felt through the lateral part of the vaginal fornix.
Ø Vaginal artery – passes across the floor of the pelvis, inferior to the ureter. The vaginal artery supplies the vagina and the urinary bladder.
Ø Note that the vaginal artery and the uterine artery occasionally arise from one common trunk.
Ø Observe that the ureter passes between the vaginal artery and the uterine artery. We often use the mnemonic device “water under the bridge” to recall this relationship (the “water” is urine; the “bridge” is the uterine artery).
IN THE CLINIC: Uterine Artery
The close proximity of the ureter and the uterine artery near the lateral fornix of the vagina is of clinical importance. During hysterectomy, the uterine artery is tied off and cut. The ureter may be unintentionally clamped, tied off, and cut where it crosses the uterine artery. This would have serious consequences for the corresponding kidney.
MALE SUPERFICIAL AND DEEP PERINEAL POUCHES
The structural anatomy of the penis will be studied. The contents of the superficial perineal pouch will be identified. The contents of the deep perineal pouch will be described, but you will not be asked to identify these structures in any detail. Note that the following figures illustrate a cadaver for which the pelvis has not been bisected. These figures will aid you in understanding the relations between structures on either side of the midline.
Overview of the Structure of the Penis
The penis consists of three cylindrical erectile bodies. One longitudinal half of each erectile body is deep to the skin in the superficial perineal pouch, while the other halves compose the portion of the penis that can be examined externally. The three halves of the erectile bodies located in the superficial perineal pouch are collectively referred to as the root of the penis. The portion of the penis that can be examined externally is referred to as the body of the penis.
Structures in the Superficial Fasciae of the Penis
Study a drawing of a transverse section of the body of the penis (L. penis, tail) (Figure 5.13). The superficial fascia of the penis (dartos fascia) has no fat, and contains the superficial dorsal vein of the penis. The deep fascia of the penis (Buck's fascia) is an investing fascia. Also invested within the deep fascia of the penis are the deep dorsal vein of the penis (unpaired), dorsal artery of the penis (paired), and dorsal nerve of the penis (paired).
1. Note that the penis has been bisected in the cadaveric pelvis. The penis has been transected in some hemi-pelves but not others. The skin has been removed from the body of the penis by detaching it around the corona of the glans (Figure). The glans has not been skinned.
2. The superficial dorsal vein of the penis can be found in the superficial fascia of the penis. The superficial dorsal vein of the penis usually appears as a plexus of veins directly deep to the skin. The superficial dorsal vein of the penis drains into the superficial external pudendal vein of the inguinal region.
3. On the dorsum of the penis (Figure 5.14), in the deep fascia of the penis, identify the:
4. Trace the vessels and nerves of the penis proximally. Use an illustration to study the course of the pudendal nerve and the internal pudendal artery. Observe that the dorsal artery and dorsal nerve of the penis course deep to the perineal membrane before they emerge onto the dorsum of the penis. Note that the deep dorsal vein does not accompany the dorsal artery of the penis and dorsal nerve of the penis proximal to the body of the penis.
Spongy Urethra, the Corpus Spongiosum, and the Corpora Cavernosa
Contained within the deep fascia of the penis are the three halves of the erectile bodies composing the body of the penis: the corpus spongiosum, and the right and left corpora cavernosa (Figure 5.13 and Figure 5.14). The male urethra consists of three portions: the prostatic urethra, membranous urethra, and the spongy urethra (Figure 5.15). The spongy urethra is the portion that is located within the corpus spongiosum penis.
Contents of the Superficial Perineal Pouch in the Male
The contents of the superficial perineal pouch in the male are the root of the penis and three paired muscles (superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles). The superficial perineal pouch also contains the branches of the perineal arteries, veins, and nerves that supply these structures. As described above, the component of the root of the penis that is continuous with the corpus spongiosum penis is the bulb of the penis, an unpaired midline structure (Figure 5.12B). The components of the root of the penis that are continuous with the left and right corpora cavernosa penis are the left and right crura of the penis (singular: crus). Note that the portions of the three erectile bodies composing the root of the penis are separated within the superficial perineal pouch. Distally, the erectile bodies converge to form the body of the penis.
IN THE CLINIC: Superficial Perineal Pouch
If the urethra is injured in the perineum, urine may escape into the superficial perineal pouch. The urine may spread into the scrotum and penis, and upward into the lower abdominal wall between the membranous layer of the abdominal superficial fascia (Scarpa's fascia) and the aponeurosis of the external oblique muscle (Figure 5.11B). The urine does not enter the thigh because the membranous layer of the superficial fascia attaches to the fascia lata, ischiopubic ramus, and posterior edge of the perineal membrane.
4. Find the bulbospongiosus muscle in the midline of the urogenital triangle (Figure 5.12A). The bulbospongiosus muscle covers the superficial surface of the bulb of the penis. Note that this muscle will be absent in some cadaveric pelves where it was stripped off to reveal the underlying bulb of the penis. In still other cases, the muscle will be present, but can be reflected to reveal the bulb. The posterior attachments of the bulbospongiosus muscle are the bulbospongiosus muscle of the opposite side (in a midline raphe) and the perineal body. The anterior attachment of the bulbospongiosus muscle is the corpus cavernosum penis. The bulbospongiosus muscle compresses the bulb of the penis to expel urine or semen.
5. Lateral to the bulbospongiosus muscle is the ischiocavernosus muscle (Figure 5.12A). The ischiocavernosus muscle covers the superficial surface of the crus of the penis. Note that this muscle will be absent in some cadaveric pelves where it was stripped off to reveal the underlying crus of the penis. In still other cases, the muscle will be present, but can be reflected to reveal the crus. The proximal attachment of the ischiocavernosus muscle is the ischial tuberosity and the ischiopubic ramus. The distal attachment of the ischiocavernosus muscle is the crus of the penis. The ischiocavernosus muscle forces blood from the crus of the penis into the distal part of the corpus cavernosum penis.
6. The superficial transverse perineal muscle is located at the posterior border of the urogenital triangle (Figure 5.12A). The lateral attachments of the superficial transverse perineal muscle are the ischial tuberosity and the ischiopubic ramus. The medial attachment of the superficial transverse perineal muscle is the perineal body. The perineal body is a fibromuscular mass located anterior to the anal canal and posterior to the perineal membrane that serves as an attachment for several muscles. The superficial transverse perineal muscle helps to support the perineal body.
7. In the small triangular space between the bulbospongiosus and ischiocavernosus muscles in the superficial perineal pouch (Figure 5.12A), or between the crus and bulb of the penis if the muscles have been removed (Figure 5.12B), look for a white membrane. The membrane that is visible in this space is the inferior fascia of the urogential diaphragm (perineal membrane). The perineal membrane is the deep boundary of the superficial perineal pouch and the superficial boundary of the deep perineal pouch (recall that in the perineum, superficial is inferior; deep is superior). The bulb and crura of the penis are attached to the perineal membrane.
8. Identify the bulb of the penis (Figure 5.12B). Verify that the bulb of the penis is continuous with the corpus spongiosum penis and contains a portion of the spongy urethra.
9. Identify the crus of the penis (Figure 5.12B). Verify that the crus of the penis is continuous with the corpus cavernosum penis.
Contents of the Deep Perineal Pouch in the Male
The deep perineal pouch lies superior (deep) to the perineal membrane (Figure 5.15). The contents of the deep perineal pouch in the male (Figure 5.16) include the membranous urethra, external urethral sphincter muscle, bulbourethral glands, the dorsal artery of the penis (a branch of the internal pudendal artery), and the dorsal nerve of the penis (a terminal branch of the pudendal nerve).
The Scrotum, Testes and Spermatic Cord
The scrotum is an outpouching of the anterior abdominal wall, and most layers of the abdominal wall are represented in its structure (Figure 5.7). The superficial fascia of the scrotum contains no fat. Instead, the superficial fascia is represented by dartos fascia, which contains smooth muscle fibers (dartos muscle). The scrotum has been opened by a vertical incision along its anterior surface. Observe that the scrotal septum divides the scrotum into left and right compartments. The spermatic cord will be followed from the superficial inguinal ring into the scrotum.
The spermatic cord contains the ductus deferens, testicular vessels, lymphatics, and nerves. The contents of the spermatic cord are surrounded by three fascial layers, the coverings of the spermatic cord, which are derived from layers of the anterior abdominal wall (Figure 5.7). These coverings are added to the spermatic cord as it passes through the inguinal canal.
IN THE CLINIC: Vasectomy
The ductus deferens can be surgically interrupted in the superior part of the scrotum (vasectomy). Sperm production in the testis continues but the spermatozoa cannot reach the urethra.
The testis is covered by the tunica vaginalis (Figure 5.7), a serous sac that is derived from the parietal peritoneum (i.e., the portion of the peritoneum that lines the inner wall of the abdominal cavity as opposed to the organs). The cavity of the tunica vaginalis is only a potential space that contains a very small amount of serous fluid. The tunica vaginalis (Figure 5.9) has a visceral layer (lining the testis) and a parietal layer (lining the walls of the cavity of the tunica vaginalis). Note that the spermatic fasciae also cover the testis, superficial to the parietal layer of the tunica vaginalis. The spermatic fasciae are very thin here and difficult to separate from the parietal layer of the tunica vaginalis.
IN THE CLINIC: Lymphatic Drainage of the Testis
Lymphatics from the scrotum drain to the superficial inguinal lymph nodes. Inflammation of the scrotum may cause tender, enlarged superficial inguinal lymph nodes. In contrast, lymphatics from the testis follow the testicular vessels through the inguinal canal and into the abdominal cavity where they drain into lumbar (lateral aortic) nodes and preaortic lymph nodes. Testicular tumors may metastasize to lumbar and preaortic lymph nodes, not to superficial inguinal lymph nodes.
[A DETAILED STUDY OF THE STRUCTURES OF THE FEMALE PERINEUM WILL BE UNDERTAKEN DURING THE INTERSESSIONS PRECEDING THE OBSTETRICS / GYNECOLOGY CLERKSHIPS]
Here we conduct a prosection study to examine the female breast and the placenta.
THE ADULT FEMALE BREAST
The breast extends from the lateral border of the sternum to the mid-axillary line, and from rib 2 to rib 6. The breast is positioned anterior to the pectoral fascia (deep fascia of the pectoralis major muscle; Figure 1). The pectoral fascia is attached to the skin by the suspensory ligaments of Cooper (Figure 2 and Figure 3). The nipple is centrally located within the pigmented areola (Figure 4). The areolar glands (sebaceous glands) lubricate the nipple and areola to facilitate nursing.
The mammary gland is a modified sweat gland that is contained within the superficial fascia of the breast. The breast consists of fibrous and adipose tissue between the lobes and lobules of glandular tissue, together with blood vessels, lymphatic vessels and nerves (Figure 2 and Figure 3). If present, the lobes of glandular tissue are radially arranged, separated by connective tissue and fat. Each lobe has its own lactiferous duct which usually opens independently on the nipple. On the nipple, find the opening of one of the 15 – 20 lactiferous ducts which converge on the nipple. Deep to the areola, each lactiferous duct has a dilated portion, the lactiferous sinus, in which a small droplet of milk accumulates or remains in the nursing mother.
NOTE: The breast specimens you are studying are from elderly women where most of the glandular tissue has been replaced by fatty tissue. In most cases there is also a decrease in total fat resulting in small and wrinkled breasts. The condition of the elderly breasts often makes it difficult to distinguish the lactiferous ducts from the suspensory ligaments. As a general rule of thumb, if the structure in question runs to the nipple, assume it is a lactiferous duct. If the structure runs to the skin, but not to the nipple, then assume it is a suspensory ligament.
Lymphatic drainage from the adult female breast (see Figure 5)
1. Numerous lymph vessels in the breast communicate in a subareolar plexus deep to and around the nipple.
2. 75% of the lymph courses laterally and upward to axillary and infraclavicular nodes.
3. Some lymph passes medially to parasternal nodes along the internal thoracic vessels
4. Some lymph drains downward to abdominal nodes or to the opposite breast.
Breast cancer is the most common malignancy in women. Almost two thirds of all cases occur in postmenapausal women. For the anatomical location and description of tumors, the breast is divided into 4 quadrants (Figure 6), upper inner (UI), upper outer (UO – contains a large amount of glandular tissue which often extends an axillary tail), lower inner (LI) and lower outer (LO) quadrants. Approximately 50% of cancers develop in the upper outer quadrant. Metastatic involvement of lymph nodes usually occurs in the axilla.
Clinical signs of breast cancer:
1. Vascular signs (Figure 7) – A fast growing tumor with large vascular demand may cause dilation of superficial veins, creating a prominent vascular pattern over the breast.
2. Nipple retraction (Figure 8) – Carcinomatous involvement of mammary ducts may cause duct shortening and retraction or inversion of nipple.
3. Skin dimpling (Figure 9) – Dimpling of skin over a carcinoma is caused by involvement and retraction of the suspensory ligaments (of Cooper).
4. Skin edema (Figure 10) – Involvement and obstruction of subcutaneous lymphatics by a tumor can result in lymphatic dilatation and lymph accumulation in the skin. The resultant edema creates a “orange peel” appearance (or “peau d’orange” sign) due to prominence of skin gland orifices.
THE FULL TERM PLACENTA
The FULL TERM PLACENTA is a flattened discoidal mass with a circular or oval outline. It has a diameter of 15 – 20 cm, a thickness of 3 cm and weighs about 500 g. On the specimens, identify the features of the placenta that are bolded. The fetal surface (Figure 1 and Figure 2) is covered by the amnion which is smooth, shiny and transparent. The subjacent chorion is mottled in appearance and can be seen through the filmy amnion. The umbilical cord is usually attached near the center of the fetal surface. The branches of the umbilical vessels radiate out under the amnion. The veins are larger and deeper than the arteries (the difference is subtle – don’t try to distinguish the vessels in this manner). Note that the cord shows a marked torsion due to fetal movement or unequal growth of the umbilical vessels. Figure 3 shows the spiral twisting of the arteries and the presence of constrictions. On the cut edge of the cord, identify two umbilical arteries and one umbilical vein.
The maternal surface appears finely granular and is made up of 10 – 30 convex cotyledons separated by grooves formerly occupied by maternal placental septa (Figure 4). Each cotyledon consists of two or more main stem villi and their many branches. A number of fetal cotyledons form a placental lobe, which corresponds to the major branches of distribution of the umbilical arteries (Figure 5). The surface of the cotyledons may be incompletely covered by a thin layer of decidua basalis.
FOCUS QUESTIONS and ANSWERS
1. 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?
2. Define the rectum.
3. Define and note the flexure between rectum and anal canal. What muscle assists in maintaining this flexure?
4. On the sagittally-sectioned female specimen, trace the peritoneum from the ventral abdominal wall; examining the vesicouterine pouch and its manner of reflection from the bladder to the uterus. Onto what part of uterus does it reflect?
5. Trace the peritoneum across the uterus and define the rectouterine pouch. Note peritoneum on the posterior wall of the vagina. From what point does the peritoneum reflect to the rectum? What is the significance of this?
6. Within the broad ligament, locate the ovarian ligament and the round ligament of the uterus. Consider development and continuities of these structures.
7. Locate and define the peritoneal fold called the suspensory ligament of the ovary. What does it contain?
8. Strip the peritoneum from the suspensory ligament of the ovary on one side and trace the ovarian artery and vein. What are their sources?
9. What is the complete area of distribution of the ovarian artery?
10. Locate a ureter. Note its relation to uterine artery. Trace it to the bladder and posteriorly to the brim of the pelvis, noting course, relation to peritoneum, and blood supply.
11. Trace the round ligament from the uterus to the deep inguinal ring. Where does it attach?
12. What structures support the uterus?
13. Explore the female urethra, noting length, sphincter muscle, and relation to vagina. Note specifically the relation of the orifice to the anterior vaginal wall. What is the significance ?
14. Define the ampulla of the ductus deferens. Is it covered by peritoneum?
15. What is the rectovesical pouch?
16. Where does the transition of the epididymis to the ductus deferens occur?
17. Locate the anterior division of the internal iliac artery and note how it terminates by dividing into the inferior gluteal and the internal pudendal arteries. These exit the pelvis below the lower border of the piriformis muscle. What are other relations?
18. Do you have an "aberrant obturator artery", which arises from the inferior epigastric artery and accompanies the obturator nerve?
19. Locate the sympathetic trunk entering the pelvis along the medial border of the pelvic sacral foramina. Note number of ganglia, gray rami communcantes, and sacral splanchnic nerves.
20. How many pelvic splanchnic nerves are there?
21. Do you find muscular (deep) branches of the perineal nerves?
22. 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?
23. What is the function of the perineal membrane?
24. What is the source of the deep (central) artery of the clitoris/penis?
25. What gland is embedded in the sphincter urethrae muscle in males?