Download UNIT 32: Divided Pelvis

UNIT 32:
Divided Pelvis
Dissection Instructions:
Instructions for splitting the pelvis:
In the MALE pelvis, locate the urinary bladder behind the pubic bones and the sigmoid colon
and rectum in front of the sacrum. Note that the peritoneum dips inferiorly between the bladder and
rectum, forming the rectovesicle pouch. To the sides of the rectum are the pararectal fossae (Plates 348,
350, 353; 3.7, 3.14C).
In the FEMALE pelvis, locate the urinary bladder behind the pubic bones and the sigmoid
colon and rectum in front of the sacrum (Plates 347, 349, 352; 3.27, 3.28, 3.31). Note that the uterus,
uterine tubes and ovary are located between the urinary bladder and rectum. To the sides of the rectum
are the pararectal fossae. Locate in the FEMALE a shallow uterovesicle fossa and a deep rectouterine
pouch/of Douglas, also called the cul-de-sac (Plate 347, 351; 3.28). This extension of the peritoneal
cavity reaches the wall of the vagina in the vicinity of the posterior fornix. Find the two-layered
extension of the peritoneum lateral to the uterus, the broad ligament (Plates 354-356, 3.29, 3.30A, 3.32,
3.38). Determine the various parts of the broad ligament. Its upper border contains the uterine tube.
Suspended from its posterior surface is the ovary; the portion above the ovary which supports the uterine
tube is the mesosalpinx/mesentery of the tube) (Plates 356; 3.30A, 3.32). The portion that supports the
ovary is the mesovarium (Plates 355; 3.30A, 3.32). Both are two-layers of peritoneum. Note the free
border of the mesovarium medial to the ovary contains the ovarian ligament, a remnant of the embryonic
gubernaculum. Lateral to the ovary, the mesovarium is thickened and extends to the pelvic brim. This is
called the suspensory ligament of the ovary and contains the nerves, blood vessels, and lymphatics of
the ovary. Locate the ovarian vessels crossing the external iliac vessels to enter the pelvis in the
suspensory ligament (Plates 351, 380; 3.28B, 3.35, 3.41). The portion of the broad ligament below the
ovary and its mesentery is called the mesometrium. Observe in the region of the cervix of the uterus that
the broad ligament sends a fold of peritoneum, the rectouterine fold/uterosacral fold, posteriorly to the
region of the rectum and sacrum (Plates 349; 3.38B, 3.39, 3.41).
In BOTH SEXES starting in the mid-line of the sacral promontory and going clockwise around
the pelvic brim, identify the various nerves and arteries in the pelvis: the median sacral artery which lies
in the mid-line or slightly to the left (It was the continuation of the dorsal aorta in the embryo) (Plates
256, 328, 380-383; 2.82, 3.4); the superior hypogastric plexus which is also in the mid-line (Plates 389,
390, 392; 2.76, 2.78, % - 3.8, 3.25, & - 3.39); the sympathetic trunk on the anterolateral aspect of the
body of the SV1 (Plates 259, 390, 392; 2.76, 2.78, 3.10, 3,23); the lumbar branch of the iliolumbar
vessels which crosses the ala of the sacrum (Plates 256, 382; 3.24, figures-pp.212 & 234); and the
anterior primary ramus of L5 and fibers from L4 which cross the pelvic brim to form the lumbosacral
trunk of the sacral plexus (Plates 259; 2.72, 2.73, 2.82B, 3.5). Locate anterior to the lumbosacral
trunk the obturator nerve. The superior rectal vessel lies in the sigmoid mesocolon or the parietal
peritoneum near the attachment of the sigmoid mesocolon (Plates 327, 378, 379; 3.10). Observe the
sigmoid colon. It is variable as it enters the true pelvis. Clean the internal iliac vessels as they enter the
true pelvis anterior to the sacroiliac joint. Also clean the ureters as they enter the pelvis (Plates 327,
328, & - 382, % - 383; 2.82D, % - 3.19A&B, 3.21A, Table 3.3 and figure-pp. 212 & 213, & - 3.31, Table
3.5 and figure-pp. 234 & 235). Find either the round ligament of the uterus or the ductus deferens as
it crosses the pelvic brim in an anterolateral position (Plates & - 257, 349, 380, % - 348, 350. 381; & 3.27, 3.28B, 3.29, 3.31, 3.32, 3.34, % - 3.8, 3.13, 3.14A, 3.19A&B). Anterior to that is a pubic branch of
the inferior epigastric artery, which frequently is enlarged to become the abnormal obturator artery
Unit 32 - 1
(Plates 251; 3.20).Identified both the medial umbilical ligament and the median umbilical ligament
(Plates 245; 3.13A&B). On the right side, the appendix frequently falls into the pelvis minor.
Actual splitting of the pelvis
Cut transversely through the soft tissues of the body at the level of the third lumbar vertebra, then
saw through the vertebral column to separate the upper part of the body from the pelvis and lower limbs.
Using a scalpel, carefully cut the soft tissues of the pelvis and perineum in the mid-sagittal plane.
Insert a probe into the urethra to be sure the penis and bladder are cut in the central plane. Cut through
the symphysis pubis with a scalpel. Straighten the uterus and vagina if they are deviated from the midline. Cut the anal canal in the mid-line, but the rectum need not be straightened. The sigmoid colon
should be on the left side of the mid-line when the cut is made. Cut the right common iliac artery and
the left common iliac vein as close to the mid-line as possible and retract the aorta toward the left side.
Insert a hand-saw between the cut surfaces until it rests on the tip of the coccyx and the
promontory of the sacrum. Cut through the vertebral column in the mid-line as exactly as possible
Solid fecal material should be placed in the waste containers, then the specimens can be washed
in the sink.
In the MALE, begin your study with the urethra. It consists of three parts: prostatic,
membranous/intermediate and spongy or penile Plates 348, 367, 368; 3.14, 3.16, 3.19). The prostatic
urethra is "U" shaped in cross-section, with the bottom of the "U" anterior which is caused by the
urethral crest. Mid-way down the crest is the colliculus seminalis, which presents three openings. The
larger, central opening is the prostatic utricle, an embryonic remnant related to the uterus. On each side
of the utricle are the openings of the ejaculatory ducts. The grooves on each side of the urethral crest are
the urethral sulci, where most of the ducts of the prostatic glands open.
The membranous urethra/intermediate urethra connects the prostatic urethra with the penile
urethra and is located in the deep perineal pouch/urogenital diaphragm (Plates 368; 3.16, 3.51). It is
the part most frequently damaged during passage of catheters and other instruments, as it is nearly at a
right angle from the penile urethra.
The urethra then enters the bulb of the penis, traveling in the corpus spongiosum to reach the
glans penis, where it ends by opening on the surface. Just before it ends, it is enlarged to form the
navicular fossa fossa(Plates 367, 368; 3.48). The bulbourethral glands open into the bulbar portion of
the urethra and other urethral glands are found along its course.
The urethra in the FEMALE is much shorter and has no special anatomical features (Plates 347,
353; 3.27, 3.28A).
In BOTH SEXES f the bladder may be relatively smooth if the bladder was distended, or very
wrinkled if it was empty. Locate the openings of the ureters and the beginning of the urethra (Plates 352,
353, 367; 3.14, 3.16, 3.28A). Between these three points is the bladder trigone. The ureters pass through
the wall of the bladder obliquely, so that as pressure builds up in the bladder, there is a valve-like
mechanism to prevent retrograde flow of urine back up to the kidneys. The side of the trigone between
ureters is usually elevated to form the interureteric crest. The posterior or median lobe of the prostate
frequently enlarges, causing an upwards bulge in the lower angle of the trigone. When present, it is called
the uvula.
Unit 32 - 2
In the MALE the prostate gland surrounds the urethra (Plates 353, 367, 368; 3.7, 3.14A-D,
3.16, 3.19A). Its base is related to the neck of the bladder and its apex rests on the top of the urogenital
diaphragm, the left and right pubococcygeous muscles being separated from each other. The ejaculatory
ducts pass through the substance of the prostate gland to reach the colliculus of the urethral crest. The
prostate has anterior, lateral, median and posterior lobes, the lateral being paired and the largest. Some
sources describe only three lobes.
The seminal vesicles lie lateral to the ampullae of the ductus deferens and inferior to the ureters
(Plates 348, 367; 3.6, 3.14A-C, 3.15). One should be opened to show that it is a convoluted tubular gland
which joins the ductus deferens to form the ejaculatory duct. On one side, follow the ejaculatory duct
through the prostate to the colliculus where it opens into the urethra.
In the FEMALE, look for mucosal folds in the lumen of the vagina (Plates 347, 352; 3.27,
3.28A). Follow the vaginal wall and note how it attaches to the cervix of the uterus. The space between
the wall of the vagina and the cervix is the fornix. The posterior fornix is the largest and is separated
from the peritoneal cavity by only the wall of the vagina and peritoneum. The anterior fornix is small and
is not related to the peritoneal cavity.
The uterine cavity communicates with the vaginal cavity through the cervical canal (Plates
352, 355, 356; 3.33). It is near the external os of the cervical canal that the epithelium changes from the
simple columnar type of the uterus to the stratified squamous type of the vagina. The internal os is at the
junction of body and cervix. The cavity of the uterus is triangular in shape when viewed from the
anterior. The base of the triangle relates to the fundus and its upper angles are where the uterine tubes
communicate with the uterine cavity. The lower angle is at the internal os. The thick wall of the uterus is
primarily myometrium. The uterus atrophies in post-menopausal women and is the frequent location of
tumors, usually benign fibroid or leiomyomas.
The uterine tubes have a narrow opening into the cavity of the uterus (Plates 356; 3.27, 3.30,
3.32, 3.33). Open one uterine tube. At its lateral end, the lumen enlarges before reaching the fimbriated
end of the tube.
In BOTH SEXES, the rectum typically has three semicircular transverse folds, the first and
last on the left side and the middle one on the right side (Plates 373-375; 3.8, 3.10B, 3.9, 3.19A). The
lumen of the rectum usually appears large, but narrows when it reaches the anal canal.
The anal canal begins at the level of the pelvic diaphragm. The puborectalis (pubococcygeous)
muscle pulls the digestive tube forward, so that the longitudinal axis of the rectum is at about a 90o angle
from the longitudinal axis of the anal canal (Plates 344, 345; 3.4, 3.6). The anal canal is only about an
inch long, but it displays several features (Plates 374, 375; 3.9, 3.10). It is covered on its outside by the
external anal sphincter, which is voluntary (Plates 375; 3.9, 3.10C). Its outer longitudinal muscle layer
becomes a fibroelastic membrane which ends by separating the subcutaneous portion of the external anal
sphincter into many different fascicles. The inner circular layer of muscle thickens to form the internal
anal sphincter, an involuntary sphincter. The mucosa and submucosa form a series of vertical anal
columns and sulci. The sulci end inferiorly in a blind sac and the columns are connected inferiorly by the
anal valves. The epithelium to this point is simple columnar. Below the level of the anal valves is a
transitional zone, followed by a cutaneous zone with hair and glands.
Review the branches of the internal iliac artery and confirm the names of these branches by
following and cleaning them to their destinations (Plates 378, 380, & - 382, % - 383; 3.19, % - Table 3.3
and figure-pp. 212-213, & - Table 3.5 and figure-pp. 234-235). Envision the lymphatic pathways
Unit 32 - 3
(Plates 386, 388; 3.36, 3.37, 3.50A Locate the pelvic splanchnic nerves (nervi erigentes) passing from
sacral nerves 2, 3 and 4 and entering the pelvic or inferior hypogastric plexus (Plates 390, 392; 3.24,
3.25A, 3.39). Look carefully for sacral splanchnic nerves passing from the sympathetic trunk to the
pelvic plexus. Follow the inferior hypogastric plexus into the plexuses on the organs in the pelvis.
Identify the L4 contribution to the lumbosacral trunk and the anterior/ventral primary rami
of L5, S1, 2, 3 and 4 (Plates 481; 3.24, 3.26, Table 3.4 and figures-p. 223). They combine to form the
sacral plexus and pudendal nerve. The superior gluteal artery usually passes between the lumbosacral
trunk and the first sacral nerve. The inferior gluteal artery is more variable and may pass between the
first and second or second and third sacral nerves. Between the gluteal arteries and posterior to the sacral
plexus is the piriformis muscle. This muscle takes origin from the anterior surface of the sacrum and
passes through the greater sciatic foramen to insert on the greater trochanter of the femur. It is a lateral
rotator of the thigh. If you pull the sacral plexus forward off the piriformis, you will find the nerve to the
piriformis coming from the first two sacral nerves.
Clean the surface of the pelvic diaphragm and identify its various parts (Plates 344, 345; 3.43.6, 3.24, Table 3.2 and figures-p.193). Spare its nerve supply, which lies on its superior surface, after
arising from the third and fourth sacral nerves. Make sure the ischiorectal fossa is cleaned of fat so that
you can isolate the diaphragm both superiorly and inferiorly. Establish that the arcus tendinous is a
thickening of the obturator fascia. Identify the pudendal nerve and internal pudendal artery as they
leave the greater sciatic foramen and find them again below the pelvic diaphragm as they enter the
pudendal canal through the lesser sciatic foramen.
The transversalis fascia of the abdominal cavity is continuous with the endopelvic fascia in
the pelvis (Plates 351; 3.13). The obturator fascia and superior fascia of the pelvic diaphragm belong
to the endopelvic fascia. The endopelvic fascia is continuous with the visceral fascia (adventitia) of the
visceral organs in the pelvis.
Unit 32 - 4
Be sure to identify all of the following in this unit:
In both sexes
bladder
bladder trigone
openings of ureters
rectum
transverse folds of rectum
anal canal
external anal sphincter
internal anal sphincter
anal columns
anal sinus/sulci
anal valves
pectinate line
internal iliac artery and its branches
superior gluteal artery
inferior gluteal artery
internal pudendal artery
pelvic splanchnic nerves
inferior hypogastric plexus
lumbosacral trunk
S1, S2, S3, & S4 anterior primary rami
pudendal nerve
piriformis muscle
nerve to piriformis muscle
pelvic diaphragm
arcus tendinous of obturator fascia
transversalis fascia
endopelvic fascia
obturator fascia
On the Male split pelvis
urethra
prostatic
membranous/intermediate
spongy/penile
urethral crest in prostatic urethra
seminal colliculus
prostatic utricle
ejaculatory ducts
urethral sulci
ducts of prostatic glands
penile urethra
bulb of penis
corpus spongiosum
glans penis
navicular fossa
prostate gland
On the female split pelvis
urethra
vagina
fornix
posterior fornix
uterus
cervix
body
uterine cavity
internal os of uterus
external os of uterus
myometrium
opening of uterine tube into uterus
uterine tube
fimbriated end of the tube
Unit 32 - 5