Dissection 5. Pelvis and
This guide to dissection replaces
the assigned pages in Grant's Dissector. Its goals are: l ) to orient you
and prepare you in advance for this dissection, and 2) to take you through
the dissection in an orderly and logical way, highlighting important structural
and functional relationships in the pelvis and perineum. The guide is divided
into two parts: 1. A self-instructional module which should be used to
acquaint you with the three-dimensional orientation of the region. 2. Instructions
for carrying out the dissection of the pelvis and perineum.
Remember that, although you will
only be responsible for dissecting one cadaver, you are expected to acquire
a reasonable understanding of the pelvis and perineum in both sexes.
You should therefore read through the orientation and instructions for
dissection in both sexes. Make sure that you examine cadavers of both sexes
when the dissections are complete.
Part 1. Orientation and guide
to the anatomy of the pelvis and perineum: a self-instructional module.
You should work your way through
the material contained in this self instructional module before you
attempt the actual dissection of the pelvis and perineum. The best time
for you to do this will be during the week before your assigned dissecting
time, i.e. while the A-team is completing its dissection of the abdomen.
If you attempt the dissection without completing the self-instructional
module you will waste considerable time and effort, as well as subjecting
yourself to a great deal of frustration.
Space and a relatively quiet and
odor-free atmosphere for your work will be provided in Rooms 337 and 338
of the Anatomy-Physiology Building. You will need to have access to an
articulated pelvis to complete this self-instructional module. You will
also find it helpful to have string, tape, paper and scissors. These will
be available in Rooms 337 and 338. The single os coxa and sacrum provided
in your bone box may also be useful for orientation. Please remember to
treat all skeletal materials and articulated pelves with care. DO NOT MAKE
MARKS ON DISARTICULATED BONES OR ARTICULATED PELVES. You may, however,
use paper, tape and string on the bones as long as they are carefully removed
when you are finished with this exercise. HANDLE THE ARTICULATED PELVES
MADE OF REAL BONE WITH EXTREME CARE. THESE ARE VERY FRAGILE.
Start by becoming familiar with the
correct anatomical orientation and bony parts of an articulated pelvis.
The orientation of the pelvis with the body in the upright position is
with the anterior superior iliac spine and the superior part of
the pubic symphysis in a vertical plane, as shown below.
Figure 1. Orientation of the pelvis
in the upright position. View of the right side of the pelvis. (From: Grant's
Atlas, Fig. 3.9.)
You can verify that this is the correct
orientation by palpating these bony landmarks on yourself or another student
while in the upright position, or by looking at an articulated skeleton.
Next, viewing the bony pelvis from
the front (anterior view) (see Fig. 2 below), verify for yourself the following
1. The bony pelvis is made up of
Figure 2. Frontal view of bony pelvis.
(Modified slightly from: Snell. Clinical Anatomy for Medical Students.
Figure 5b, p. 260.)
2 os coxae or innominate bones: These
are formed from 3 separate bones which fuse around the 16th year of life:
the ilium, the ischium. and the pubis. These are names which are used to
designate particular parts of the fused os coxae in the adult. (See Fig.
1 sacrum: Formed from 5 sacral vertebrae
which fuse. On its ventral surface are 4 pairs of foramina through which
the ventral primary rams of sacral nerves exit. (See Fig. 4 below.) On
its dorsal surface are 4 pairs of foramina through which the dorsal rami
of sacral nerves exit. (See Fig. 5 below.)
1 coccyx: Formed from 4 fused vertebrae.
Figure 3. Lateral view of right os coxa.
(From: Snell, Clinical Anatomy for Medical Students. Fig. 12b, p. 266.)
Figure 4. (left) Ventral (anterior)
view of the sacrum and coccyx. (Modified slightly from: Snell, Clinical
Anatomy for Medical Students. Fig. 9a, p. 263).
Figure 5. (right) Dorsal (posterior)
view of the sacrum and coccyx. (Modified slightly from Snell, Clinical
Anatomy for Medical Students. Fig. 9b, p. 263).
Figure 6. Joints of the pelvis indicated
on frontal view of bony pelvis. (Modified slightly from: Snell, Clinical
Anatomy for Medical Students, Fig 5b, p. 260.)
Now that you are familiar with the
bony composition and major joints of the pelvis, you should make sure you
can readily identify the following bony landmarks on an articulated pelvis,
since they will be important in discussing pelvic anatomy. Use Figs. 7-8
below for orientation.
Figure 7. Frontal view of the bony pelvis
indicating major bony landmarks 1-7 above. (Modified slightly from: Snell,
Clinical Anatomy for Medical Students, Fig. 5a, p.260.)
The pelvic inlet or pelvic
brim: a bony rim made up of the sacral promontory, the iliopectineal
line and the superior border of the svmphysis pubis.
The pubic tubercle(s).
The obturator foramina.
The pubic arch (made up of a
right and a left ramus).
The ischial tuberosities: verify
on yourself that this is the part you sit on.
The ischial spines.
The acetabulum. A Unshaped socket
which articulates with the head of the femur (see Fig. 3).
Figure 8. Inferior view of the outlet
of the bony pelvis. (Modified slightly from Woodburne, Essentials of Human
Anatomy, Figure 375, p. 465)
The pelvic outlet: A diamond-shaped
area, best appreciated when viewed from below. The boundaries of the pelvic
outlet are: the pubic symphysis, right and left rami of the pubic
arch, the ischial tuberosities, the sacrotuberous ligaments
(described below) and the tip of the coccyx.
In the living person (or the intact
cadaver) there are 2 important ligaments which help to stabilize the bony
Figure 9 (left). Frontal view of the
bony pelvis illustrating the disposition of the sacrotuberous and sacrospinous
ligaments on the right side. (Modified slightly from: Snell, Clinical Anatomy
for Medical Students, Fig. 5a, p.260.)
The sacrospinous ligament.
The sacrotuberous ligament.
Figure 10 (right). Dorsal (posterior)
view of the right side of the bony pelvis, showing the disposition of the
sacrotuberous and sacrospinous ligaments. (Modified slightly from: Basmajian,
Grant's Method of Anatomy, Fig. 17.21, p.215.)
Using paper and tape or string and
tape construct a facsimile of these two ligaments on the articulated pelvis.
Note that these two ligaments define the boundaries of the greater and
lesser sciatic foramina (see Fig. 10 above). Important nerves, blood vessels
and muscles pass through these foramina, so you must become familiar with
their location and boundaries.
The area lying between the pelvic
inlet and the pelvic outlet is considered to be the true Pelvis, or pelvic
cavity. The area above the pelvic inlet is sometimes termed the false pelvis,
but a quick look at an articulated skeleton or a partially dissected cadaver
will show you that this region is really part of the abdominal cavity.
You have now defined the bony and
ligamentous framework of the pelvis (above), without consideration of bony
differences between males and females. Although many texts delineate these
differences ad nauseum, the important differences between male and female
peIves are summarized very succinctly in Fig. 11 below.
Figure 11. Table summarizing the differences
in the shape of the pelvic inlet, pelvic outlet, pelvic cavity and pubic
arch in male and female pelves. (From Snell, Clinical Anatomy for Medical
Students. Fig. 20 p.075.)
Verify these differences in typical
shape of male and female bony pelvis by referring to Figs. 3-1 through
3-4 Grant's Atlas. Attempt to obtain both male and female articulated bony
pelvis and compare the features highlighted in Fig. 11 above.
Although it is important to understand
the architecture of the bony pelvis, you should realize that the walls
of the pelvic cavity are formed not only by bones and ligaments, but also
by muscles. Two muscles and their fasciae form part of the walls of the
Fig. 12 (left). Disposition of piriformis
(shown) Fig. 13. Dorsal (posterior) view of right side on right side of
pelvis) and coccygeus of bony pelvis showing insertions of obturator muscles
shown in frontal view of bony internus and piriformis muscles onto greater
The piriformis muscle: Takes
origin from the front of the sacrum near the 3rd and 4th sacral foramina.
The muscle leaves the pelvis by passing laterally through the greater sciatic
foremen and inserts on the upper border of the greater trochanter of the
femur. (See Figs. 12 and 13 below, also Atlas Figures 3-12 and 4-36.)
The obturator internus muscle:
Takes origin from the inner surface of the obturator membrane, which closes
over most of the obturator foremen, and from the interior surfaces of the
pubis and ischium, below the Iliopectineal line, and from the pubic ramus.
This is a fan-shaped muscle which becomes tendinous as it passes through
the lesser sciatic foremen. The tendon inserts on the greater trochanter
of the femur. (See Figs. 13 and 14 below, also Atlas Figures 3-12, 3-22,
Fig. 13 (right). Dorsal (posterior)
view of right side of bony pelvis showing insertions of obturator internus
and piriformis muscles onto greater trochanter of the femur.
Figure 14. Illustrates the origin of
the obturator internus muscle. This is a view of the right side of the
pelvis, looking at the pelvic walls from the midline. The insertion of
the obturator internus tendon on the greater trochanter is illustrated
in Fig. 13. Note also that the position of line of attachment of the levator
ani muscle and the approximate position of the pudendal canal in the obturator
internus fascia are indicated. These will be described in more detail below.
Two muscles and their fasciae form
the floor of the pelvic cavity, which is also referred to as the pelvic
Try not to become so fixated on defining
parts of the levator ani that you forget that the levator ani is basically
one muscular sheet.
The levator ani muscle: This
is a thin sheet of muscle which takes origin from the pubic bone and the
adjacent fascia of the obturator internus muscle (see Figs. 15 and 16 below,
and Atlas Figure 3-121. Various portions of this muscular sheet insert
respectively, on the coccyx; onto a fibrous band running from the rectum
and coccyx called the anococcygeal rapine; and onto a fibrous body
lying between the prostate or vagina and rectum, known as the perineal
body. The levator ani muscle can be subdivided, depending on the exact
origin and insertion of the fibers:
levator prostatae or sphincter
vaginae - These include the fibers taking origin from the posterior
surface of the pubis, and inserting in the perineal body. These form a
"sling" around the prostate or vagina. (Not shown in the figures, except
Snell, Fig. 15, p. 269.)
puborectalis - These fibers take
origin from the posterior surface of the pubis, and form a sling around
the rectum. The puborectalis is thought to be important in maintaining
fecal continence. (See Atlas Fig. 3-40.)
pubococcvgeus - These fibers
take origin from the posterior surface of the pubis and insert into the
iliococcvgeus - these fibers
take origin from the obturator internus fascia and ischium and insert
into the anococcygeal rapine.
Figure 15. (left) Schematic drawing
showing the attachment of the levator ani muscle to the obturator internus
fascia. (From Basmajian, Grant's Method of Anatomy, Fig. 17.6, p. 209.)
Figure 16. (right) Drawing summarizing
the arrangement of muscles forming the floor and walls of the pelvic cavity.
Note that the levator prostatae (sphincter vaginae) portion of the levator
ani muscle is not shown. (From: Woodburne, Essentials of Human Anatomy,
Fig. 405, p. 512.)
Figure 16 above summarizes the disposition
and relationships of the obturator internus, piriformis, coccygeus and
levator ani muscles in forming the muscular floor and walls of the pelvis.
(Atlas Figs. 3-12 and 3-13 also serve as good summary figures.
The coccvgeus muscle: This muscle
takes origin from the ischial spine and inserts onto the lower part of
the sacrum and coccyx. Its disposition is illustrated in Fig. 12. Note
that the orientation and shape of the coccygeus muscle are parallel to
those of the sacrospinous ligament, but the muscle lies anterior (ventral)
to the ligament. (This point is also demonstrated very clearly by comparing
Atlas Figures 3-55 and 3-57.)
Probably the best way to appreciate
the orientation and relationships of the muscles forming the floor and
walls of the pelvis is to place paper representations of the muscles in
the appropriate positions on an articulated pelvis. To facilitate this
exercise, paper templates of these muscles are provided on thelast 2 pages
of this guide. Note that for the piriformis, coccygeus, and obturator internus
muscles, templates are provided for the muscles on the right of the
pelvis only. (To construct muscle models for the left side. make a
mirror image copy of the template for the right side.) Muscles will be
correctly oriented if you place them in the bony pelvis with the writing
facing the interior of the pelvis. Orient the muscles correctly using the
descriptions and figures provided above. Hold the "muscles" in place with
tape. Note that the obturator internus and piriformis muscles attach to
the greater trochanter of the femur in real life. Since you don't have
femurs furnished with your articulated pelves, it will be best for you
to attach these "muscles" at the acetabulum. The large black dots drawn
on the template indicate the approximate position where you should attach
the piriformis and obturator internus muscles to the acetabulum to achieve
the correct position and orientation. Note that since bony pelves differ
somewhat you may have to fidget, a bit to make the paper muscles fit on
your bony pelvis.
When you feel comfortable with the
architecture of the pelvic walls and floor, it is time to move on to a
consideration of the regional anatomy of the pelvis. Before considering
the anatomy of the pelvis itself, however, it will be appropriate to briefly
consider the relationship of the pelvis to the adjoining regions of the
body: the abdominal cavity and the lower limb.
It was noted above that the official
definition of the pelvis states that the pelvis comprises the area between
the pelvic brim (or inlet) and the pelvic outlet. This area can be subdivided
into the area above the pelvic diaphragm, termed the pelvic cavity proper;
and an area below the pelvic diaphragm, termed the perineum (See
Figure 17. Schematic drawing of the
pelvis showing how the pelvic diaphragm subdivides it into the pelvic proper
and the perineum. (From: Moore, Clinically Oriented Anatomy, Fig. 3-51,
I. Relationship of the pelvis
to the abdominal cavity.
Figure 18. Diagram illustrating the
continuity of the abdominal and pelvic cavities. The (thoracoabdominal)
diaphragm forms the roof of the abdominopelvic cavity, pelvic diaphragm
forms its floor (modified from: Moore' Clinically Oriented Anatomy, Fig.
3-51, p. 342.)
You should realize from the dissection
you have done thus far that the pelvic cavity proper is simply an inferior
continuation of the abdominal cavity. In fact, the abdominal and pelvic
cavities are sometimes considered as a single cavity (termed the abdominopelvic
cavity) with the thoraco-abdominal diaphragm forming the roof and the pelvic
cavity forming the floor (Fig. 18). It makes sense, therefore, that certain
of the organ systems of the abdominal cavity are continued in the pelvic
cavity: the pelvic cavity contains the terminal portions of the gastrointestinal
tract (sigmoid colon and rectum) and the urinary system (ureters, bladder,
and beginning portion of the urethra). The peritoneum also continues into
the pelvis, partially covering the pelvic organs, and forming various ligaments
and mesenteries as it drapes over vasculature and other structures passing
from the pelvic walls to the viscera. It is important to realize, however,
that the peritoneum does not reach all the way to the lowest points of
the pelvic diaphragm so that there exists a fairly substantial subperitoneal
space containing varius pelvic organs (or portions of pelvic organs),
vasculature, and fascial ligaments which play an important role in supporting
Figure 19. Diagram illustrating the
continuation of the peritoneal cavity into pelvis, and the existence of
a substantial subperitoneal space between the peritoneal and the pelvic
Logically, the major arterial trunks
seen in the abdominal cavity will also be continued into the pelvis, while
major veins and lymphatic trunks seen in the abdomen will receive blood
or lymph from tributaries located in or near the pelvis. Some of the nerves
seen in the abdomen also continue into the pelvic cavity. Let us start
by considering the arterial blood supply to the pelvis, relating it to
what you already know (hopefully) about arteries in the abdomen.
Figure 20. Schematic diagram illustrating
the sources of arterial blood supply to pelvic structures.
The major artery of the abdomen
is the descending aorta. It gives off 3 unpaired visceral stalks which
supply the gastrointestinal tract (celiac trunk, superior mesenteric artery,
and inferior mesenteric artery). These mainly supply abdominal viscera,
and Hey the inferior mesenteric artery has any branches which supply
the pelvis. The superior rectal artery branches off of the inferior
mesenteric, crosses the pelvic brim, and supplies the upper part of the
rectum. You may also recall that because the ovaries and testes have an
embryonic origin near the kidneys, the arteries which supply these gonadal
organs arise from the abdominal aorta. The ovaries and testes take their
blood supply with them as they migrate. Since the testes migrate through
the inguinal canal to the scrotum, the testicular artery is not seen in
the pelvis. However, as the ovaries descend into the pelvis, they drag
the ovarian artery with them across the pelvic inlet, and into the
The abdominal aorta ends by bifurcating
at L4, to form right and left common iliac arteries. The common iliac arteries
bifurcate again just above the level of the pelvic inlet to form an internal
iliac and an external iliac artery. The external iliac artery passes under
the inguinal ligament into the thigh; its branches constitute the major
arterial blood supply to the lower limb. The internal iliac crosses the
pelvic brim to enter the pelvis. The branches of the internal iliac
artery constitute the major blood supply to the perineum. The only
pelvic organs that don't receive their blood supply from branches of the
internal iliac are the ovaries and the superior part of the rectum. (See
Figure 20 for a summary of the points made above.)
The venous drainage of the pelvis
parallels the pattern of the arterial blood supply. Thus, most of the pelvic
cavity proper and perineum is drained by tributaries of the internal iliac
veins, which drain into the common iliac veins, which drain into the inferior
vena cave. The exceptions to this general rule should be obvious if you
think about it. First, recall that the structures supplied by branches
of the celiac trunk, superior mesenteric artery and inferior mesenteric
artery drain into the portal vein. The upper part of the rectum, supplied
by the superior rectal branch of the inferior mesenteric artery, will therefore
drain into the portal vein by way of the superior rectal and inferior mesenteric
veins. Second, the ovaries drain by way of ovarian veins into the inferior
vena cave or renal vein.
Lymphatic drainage of a region also
generally follows the pattern of venous drainage. Therefore, for the pelvis,
most of the pelvic cavity proper drains into nodes located around the internal
iliac vessels. These in turn drain into common iliac nodes, which drain
into para-aortic nodes. There are exceptions, however. Logically, the lymphatic
drainage of the ovaries is to para-aortic nodes in the abdomen, paralleling
the blood supply. Less logically, the lymphatic drainage of the perineum
is almost entirely to nodes located in the inguinal region. (A summary
of lymphatic drainage of the pelvis and perineum is provided in Figure
Figure 21. Schematic diagram
summarizing the lymphatic drainage of the pelvis end perineum. (From: Rohen
and Yokochi, Color Atlas of Anatomy, p. 341.)
Most of the nerves seen in the abdominal
cavity do not continue into the pelvis. There are exceptions: 1) The obturator
nerve. derived from L2-4 crosses over the pelvic brim and travels in
the pelvic cavity briefly before exiting through the obturator foremen
(Its destination is the adductor compartment of the thigh). 2) There are
contributions from L4 and 5 (the Jumbosacral trunk) which cross
the pelvic brim and join up with contributions arising from SI-3 to form
the sciatic nerve. This nerve leaves the pelvis through the greater
sciatic foremen and provides the major innervation to the back of the thigh
and muscles of the leg and foot. 3) The sympathetic trunk continues to
sacral levels of the pelvis, with postganglionic sympathetic fibers joining
sacral and coccygeal nerves. Postganglionic sympathetic nerves also leave
the hypogastric plexus (located in front of the sacral promontory) to innervate
smooth muscle in pelvic viscera and vasculature.
Other nerves found in the pelvis
will be essentially native to the pelvis. Recall that the vagus nerve supplies
the gut only as far as the left colic flexure. The parasympathetic nerve
supply to the pelvis is derived entirely from S2-S4. Most of the somatic
sensory and motor supply to the pelvis is also derived from S2-S4.
Figure 22. Schematic diagram summarizing
the nerve supply to the pelvis. (From: Snell, Clinical Anatomy for Medical
Students. Fig. 16, p. 279.)
II. Relationship of the pelvis
to the lower limb.
Considering the close geographical
relationship between the pelvis and the proximal part of the lower limb,
it is logical that nerves, blood vessels, lymphatics, and muscles passing
to and from the limb must either pass through the pelvis, or very near
it. Moreover, in addition to providing support and protection for the pelvic
organs, the bones of the pelvis also act as a "girdle" or framework for
attachment of the bones and muscles supporting the lower limb. The head
of each femur articulates with the os coxa at the acetabulum (see Fig.
There are 4 major "gateways" to
the lower limb. Three of these are located in the walls of the true pelvis;
only one bypasses the true pelvis.
Figure 23. Drawing illustrating the
structures entering and leaving the pelvis through the greater sciatic
foremen. (Modified slightly from: Basmajian, Grant's Method of Anatomy,
Fig. 21.6, p. 258.)
Structures passing under the inguinal
ligament bypass the true pelvis entirely on their way to the leg. Construct
a facsimile of the inguinal ligament on your articulated pelvis by attaching
a string to the anterior superior iliac spine and the pubic tubercle. Notice
that a considerable space exists between the ligament and the bony pelvis.
In this space run several important structures.
The iliopsoas muscle, which inserts
on the femur and therefore acts to flex the thigh at the hip joint.
The femoral nerve, which is the major
nerve supplying the muscles and skin on the lateral side of the front of
The femoral artery and vein, which are
the major arterial blood supply and venous drainage
for the lower limb. There are direct continuations of the external iliac
artery and vein.
L,ymphatics draining into the inguinal
Structures passing to and from the Tower
limb by way of the obturator foremen (see Fig. 15):
The obturator nerve' which supplies
skin and muscles on the medial side of the front of the thigh.
The obturator artery and vein, which
are branches of the internal iliac artery and vein, and constitute the
main vascular supply for the medial side of the front of the thigh.
Structures passing to and from the lower
limb by way of the greater sciatic foremen (see Fig. 10):
The piriformis muscle, which inserts
on the greater trochanter of the femur (see Fig. 13 above) and acts as
an abductor of the thigh at the hip.
The superior glutea] nerves and vessels,
which pass superior to the piriformis muscle supply 3 muscles of the gluteal
and hip region: gluteus medius, gluteus minimus and tensor fascia lata.
The inferior glutea] nerves and vessels,
which pass inferior to the piriformis muscle supply
the gluteus maximus muscle.
The sciatic nerve, which is the
largest nerve in the body. (It is roughly the thickness of a
garden hose!) It exits inferior to the piriformis muscle to the skin and
muscle of the back of the thigh,
as well as the entire leg and foot (see Fig. 23)
Make sure that you can localize each
of these gateways to the lower limb on the articulated pelvis. You will
dissect the lower limb in detail later in the course. At this point you
should mainly be aware as you dissect the pelvis that some of the structures
you see in the pelvis are not "native" to the region, but are passing to
or from the lower limb.
Structures passing to and from the lower
limb by way of the lesser sciatic foremen (a minor route, see Fig.
The tendon of the obturator internus
muscle, which inserts on the greater trochanter of the femur (see Fig.
13 above) and acts as an abductor of the thigh at the hip.
III. Regional anatomy of the pelvic
If you have worked through the material
above, you Greatly know a great deal about the regional anatomy of the
pelvic cavity proper. The remainder of this exercise is intended to help
you synthesize what you have learned about pelvic anatomy, and to provide
you with a more detailed understanding of the anatomy of the pelvic cavity
proper. In terms of contents of the pelvic cavity, we will be concerned
mainly with constituents of 3 major organ systems: urinary, gastrointestinal
and reproductive. Before we go into details of these systems as they relate
to the pelvic cavity proper, it will be useful to recapitulate some general
rules as they apply to pelvic anatomy.
Let us now consider the parts of the
major organ systems located in the pelvic cavity proper:
The blood supply to the pelvic cavity
proper is mainly from branches of the internal iliac
artery and vein. Exceptions: ovarian artery' superior rectal artery (see
discussion above). (See Fig.
The lymphatic drainage of the pelvic
cavity is mainly to nodes located around the internal
iliac vessels. (See Fig. 21.)
The autonomic nerve supply to pelvic
viscera is mainly from sympathetic postganglionic fibers emerging from
the hypogastric plexus, and parasympathetic preganglionic fibers
arising from S2-S4, also called pelvic splanchnics. (Remember, parasympathetic
postganglionic neurons tend to be located
in the wails of the viscera.) (See Fig. 22.)
Recall that the greater sac of the peritoneal
cavity extends part way into the pelvic cavity.
Contents ofthe pelvic cavity may therefore be subperitoneal (retroperitoneal)
or partly or completely peritonealized.
Figure 24. Drawing illustrating a midsagittal
section of male and female pelves, showing the relative positions of the
pelvic organs and the extent of the peritoneal covering (shaded). (From:
O'Rahilly, Basic Human Anatomy, Fig. 3 1-9, p. 28 1.)
The urinary system: The pelvic cavity
proper contains the terminal portion of the ureters, the bladder, and the
beginning of the urethra. The bladder is located behind the pubic symphysis.
(See Fig. 24.)
When empty, the bladder is entierely
shielded by the pubis, but the dome rises above the pubis when the bladder
is full. The ureters gain access to the bladder by descending retroperitoneally,
crossing the pelvic brim and entering the bladder posterolaterally. (See
Fig. 25.) The urethra is located (logically) at the inferior aspect of
the bladder. It passes through the prostate gland in the male, while in
the female the shorter urethra leaves the pelvic cavity immediately through
a hiatus in the pelvic diaphragm. The vascular supply to the bladder is
by way of inferior and superior vesicle arteries and veins which are branches
of the internal iliac artery and vein. Lymphatic drainage is mainly to
internal iliac nodes, but also, to some extent, to external iliac nodes.
Sympathetic nerves pass to the bladder, but apparently they only innervate
smooth muscle in the walls of blood vessels. Contraction of the smooth
muscle in the bladder wall and the involuntary sphincter of the bladder
is regulated by parasympathetic nerves (pelvic splanchnics arising from
S2-4). Look at Figure 24 and realize that, just as the components of the
urinary system are retroperitoneal in the abdominal cavity, they are retro
- or subperitoneal in the pelvic cavity. Identify the approximate location
of the bladder and urethra in the articulated pelvis.
Figure 25. Drawing illustrating the
position of the empty bladder behind the pubic symphysis, the fact that
the dome of the bladder rises above the pubic symphysis when full, and
the entrance of the ureters into the posterolateral angle of the bladder.
Lateral view of the left side of the bladder. (From: Snell, Clinical Anatomy
for Medical Students, Fig. Sa, p. 289.)
The gastrointestinal system: The
pelvic cavity proper contains part of the sigmoid colon and the rectum,
mainly the rectum. The rectum is located posteriorly in the pelvic cavity,
in front of the body of the sacrum. Just as the upper parts of the gastrointestinal
tract have a varying relationship to the peritoneum, the pelvic portions
of the gastrointestinal tract vary in their relationship to the peritoneum.
The sigmoid colon has a mesentery and is intraperitoneal. The upper part
of the rectum is covered anteriorly and laterally by peritoneum, while
the middle part is covered only anteriorly, and the lowest part has no
peritoneal covering (see Fig. 24). The upper part of the rectum receives
its blood supply from the superior rectal artery, a branch of the inferior
mesenteric. The lower 2/3 of the rectum is supplied by branches of the
internal iliac: the middle third by the middle rectal artery; the lower
third by the inferior rectal arteries which branch off of the internal
pudendal artery in the perineum (see Fig. As).
Figure 26. Drawing illustrating the
blood supply to the rectum. (From: Basmajian, Grant's Method of Anatomy,
Fig. 17.33, p. 222.)
Venous drainage parallels the arterial
blood supply. The lymphatic drainage of the pelvic rectum is mainly to
internal iliac nodes. Sympathetic (from the hypogastric plexus) and parasympathetic
(pelvic splanchnic) nerves innervate the rectum.
In the female they are located between
the bladder and rectum (see Fig. 24). Before considering the detailed anatomy
of the pelvic reproductive organs, it will be helpful to review the overall
organization of the male and female reproductive systems. The easiest way
to do this will be to trace the path of a spermatozoa through the male
reproductive system and the path of an egg through the female reproductive
The reproductive system: male and female
internal reproductive organs are housed in the pelvic cavity. In the male
the pelvic components of the reproductive system are located behind and
beneath the bladder.
Figure 27. Drawing summarizing the male
reproductive system. (From: Hole, Human Anatomy and Physiology, Fig. 21.1,
Figure 28. Drawing summarizing the
anatomy of the female reproductive system. (From: Tortora and Anagnostakos,
Prinoiples of Human Anatomy And Physiology, Fig. 28-10, p. 720.)
Important information shout male pelvic
Important information about female reproductive
The vas deferens pass behind the prostate
The seminal vesicles also lie posterior
to the bladder, lateral to the vas deferens. (See Fig. 29 below.)
The ducts of the seminal vesicles join
up with the ductus deferens to form the ejaculatory ducts in the substance
of the prostate gland.
The ejaculatory ducts empty into the
prostatic urethra, and from that point on spermatozoa travel through the
urethra to get to the outside (or inside) world.
Secretions of 3 pairs of glands, the
seminal vesicles, prostate and bulbourethral glands are added to the substance
that is ejaculated (semen). Secretions of the seminal vesicles and prostate
seem to play an important role in sperm motility. Secretions of the bulbourethral
glands appear to be more important for lubrication during sexual arousal.
Figure 29. Drawing illustrating a posterior
view of the bladder, ductus deferens, seminal vesicles and prostate in
the male. (From: Tortora and Anagnostakos, Principles of Human Anatomy
and Physiology, Fig. 28-7, p. 717.)
Although the ovaries are completely
surrounded by peritoneum (they are intraperitoneal and have a short mesentery,
the mesovarium) when the ovarian follicle ruptures, the ovum ruptures through
the peritoneal covering into the peritoneal cavity. The ovum is
then picked up by the fimbriae at the expanded end of the uterine tube,
called the infundibulum, which are highly motile. An ovum produced by the
left ovary may be picked up by, and migrate through either the right or
left uterine tube. The uterine tubes open into the perito neat cavity.
Therefore in the female, the potential exists for infection to spread from
the uterine tubes to the peritoneal cavity.
More about the regional anatomy of
the pelvis as related to the reproductive system...
Blood supply to the intenal reproductive
Figure 30. Summary of the branches of
the internal iliac artery in the male pelvis. (From: Basmajian, Grant's
Method of Anatomy, Fig. 17.35, p.233.)
Male: The prostate receives branches
from the inferior vesicle and middle recta] arteries. The venous drainage
is noteworthy: the prostatic plexes can drain toward either the vertebral
venous plexus or toward internal iliac veins. The former route provides
a pathway for spread of prostatic cancer to the spine. (See Fig. 30 below
for a summary of the branches of the internal iliac artery in the male
Female: The ovaries are supplied
by the ovarian arteries (branches of the abdominal aorta). The uterus is
supplied by the uterine artery, which branches off of the iliac artery
(see Fig. 31, note the major anastomotic connection between ovarian and
Figure 31. Drawing summarizing the
blood supply to the female internal reproductive organs. (From: Basmajian,
Grant's Method of Anatomy, Fig. 18.10, p. 233.)
The anatomic relationship between
the ureter and uterine artery is worthy of note. The ureter passes inferior
to the uterine artery near the lateral fornix of the vagina. Care must
be taken not to clamp the ureter when tying off the uterine artery during
hysterectomy. The blood supply to the upper part of the vagina is from
vaginal branches of the uterine artery and the vaginal artery, a branch
of the internal iliac artery.
Lymphatic drainage of the internal
Male: The prostate drains toward
internal iliac nodes.
Female: Most of the uterus and upper
part of the vagina drain toward internal iliac nodes. The fundus of the
uterus is said to drain along the round ligament toward inguinal nodes.
The ovaries drain to paraaortic nodes.
Nerve supply to the internal reproductive
organs: The internal reproductive organs in male and female receive parasympathetic
innervation by way of pelvic splanchnics and sympathetic innervation by
way of branches of the hypogastric plexus.
Supports of the pelvic viscera: There
are two major supports for the pelvic viscera in male and female: the pelvic
diaphragm, and the subperitoneal fascia which lies between the pelvic diaphragm
and the lower recesses of the peritoneal sac. In the male this fascia is
condensed to form puboprostatic ligaments which help to support the prostate.
In the female this fascia is condensed to form 3 pairs of ligaments which
run between the bony pelvis and the cervix (and upper part of the vagina.
These are known as pubocervical, transverse cervical, and
sacrocervical ligaments (see Fig. 32 below).
Figure 32. Drawing showing the relative
positions of the fascial ligamentous supports of the pelvic viscera in
the female. A. As seen from below. B. A modified and highly schematic parasagittal
section through the female pelvis. (Modified from: Snell, Clinical Anatomy
for Medical Students, Fig. 14, p. 302.)
The broad ligament in the female
(there is no broad ligament in the male!) is formed by the draping of peritoneum
over the uterus, uterine tubes, ovaries, and blood vessels, nerves, lymphatics
and ligaments passing and from
these structures. Realize that the broad ligament and its specializations
do not fulfill much of a supportive function in the female. (This role
is carried out mainly by the pelvic diaphragm and subperitoneal fascia.)
The broad ligament can be subdivided
into several specialized areas and smaller ligaments. If you consider the
orientation of the female reproductive organs and associated structures
beneath the peritoneal draping, the specialized folds and ligaments visible
within the broad ligament are logical. The following structures are contained
within the broad ligament (see Figures 33 and 34):
Figure 33. Drawing illustrating the
female pelvic cavity as seen from above, with the major components of the
broad ligament. (From: Tortora and Anagnostakos, Principles of Human Anatomy
and Physiology, Fig. 28-11, p. 721.)
The uterine tubes: These generally extend
out posterolaterally from the superior part of the uterus. The broad ligament
drapes over them.
The ovaries: These are generally located
in the posterior part of the broad ligament. This means that they
are visible (and palpable) through the posterior sheet of peritoneum making
up the broad ligament.
Blood vessels passing to and from the
uterus (uterine arteries), ovaries (ovarian arteries) and uterine tube
(anastomotic connections between ovarian and uterine arteries, see
Fig. 31 ): The area of the broad ligament
near the uterus where the uterine artery passes between
two sheets of peritoneum forms a mesentery for the uterus called the
mesometrium. Similarly, the short
mesenteries containing the blood supply to the uterine tube and ovary are
known as the mesosalpinx and mesovarium, respectively. The
fold of peritoneum which drapes over
the ovarian vessels as they pass from the pelvic wall
to the ovary is known as the suspensory ligament of the ovary.
Remnants of the gubernaculum: Recall
that in the male the gubernaculum is anchored to
the inferior part of the scrotum and serves to draw the testes from the
abdomen, through the inguinal
canal, and into the scrotum during fetal development. A similar
process occurs in the female, but in
the female the round ligament is anchored in the labia
majora, and the ovaries descend only to the pelvic cavity. The ovaries
do not pass through the
inguinal canal with the gubernaculum. When the ovaries have descended to
the pelvis, part of the gubernaculum
adheres to the uterus, near the opening of the uterine tube. This remnant
of the gubernaculum, which runs from the ovary to the uterus becomes
the round ligament of the ovary (or simply the ligament of the ovary).
The remainder of the gubernaculum,
running from the uterus through the inguinal canal to the
labia majora, becomes the vestigial structure known as the round ligament
of the uterus.
Figure 34. Two schematic drawings illustrating
the parts of the broad ligament and underlying structures. A. Anterior
view, showing the derivatives of the gubernaculum ovarii on the left and
the vasculature to the ovary, uterine tube and uterus on the right. B.
A parasagittal section through the broad ligament (near the lateral border
of the uterus) illustrating its major components. (Modified from: Basmajian,
Grant's Method of Anatomy, Fig. 18.5, p. 229.)
Regional anatomy of the perineum
Look at an articulated pelvis with
paper muscles in place. Recall that the perineum is the area below the
pelvic diaphragm and is therefore best viewed inferiorly (see Figs. 1 7
and 35). The superior boundary of the perineum is formed by the pelvic
diaphragm. The walls of the perineum are formed by the obturator internus
muscle, and by the bones and ligaments defining the pelvic outlet (see
Fig. 8). Verify this on the articulated pelvis. The inferior boundary of
the perineum is formed by the skin covering this region. Seen from below,
the perineum is a diamond-shaped area, which can be subdivided into an
anterior part, called the urogenital triangle, and a posterior part,
called the anal triangle (see Fig. 35).
Figure 35. Inferior view of the pelvic
outlet, showing the bony and ligamentous boundaries of the perineum and
its subdivision into anal and urogenital triangles. (From: Woodburne, Essentials
of Human Anatomy, Fig. 375, p. 465.)
Figures 36 and 37 show the externally
visible structures of the perineum in the male and female, with the boundaries
of the anal and urogenital triangles super imposed on the drawings. Realize
that the major structures of importance in the anal triangle will be the
anal canal, its external sphincters (not visible), and nerves, blood vessels
and lymphatics passing to or from the anal canal.
The important contents of the urogenital
triangle in both sexes will include the external genitalia and underlying
erectile tissue, the lower part of the urethra, a musculofascial diaphragm
called the urogenital diaphragm (part of which acts as a voluntary
sphincter for the urethra), glands which produce a lubricating substance
(bulbourethral glands in the male, greater vestibular glands in the female),
and nerves, blood vessels, and lymphatics passing to or from these structures.
In the female, the lower part of the vagina is also situated in the urogenital
Figure 36. Inferior view showing the
externally visible structures of the male perineal region and its subdivision
into anal and urogenital triangles.
Figure 37. Inferior view showing the
externally visible structures of the female perineal region and its subdivision
into anal and urogenital triangles. (Modified from: Snell, Clinical Anatomy
for Medical Students, Fig. 37, p. 321.)
Before considering the regional
anatomy of the perineum in more detail, it will be useful to make some
general points concerning the anatomy of the perineum.
1. The somatic
nerve supply (motor and sensory) to this region comes almost entirely from
branches of the pudendal nerve. This nerve arises from S2-4 in the
pelvis, leaves the pelvic cavity proper by way of the greater sciatic foremen,
and enters the perineum below the pelvic diaphragm by way of the lesser
sciatic foremen. In the perineum, the pudendal nerve travels anteriorly
in a fascial tunnel on the surface of the obturator internus, called the
pudendal canal. Verify this by recreating the course of the pudendal nerve
on your articulated pelvis using string (see Fig. 38).
Exceptions to rule 1: The genitofemoral
nerve (Ll and 2) supplies motor innervation to the cremaster muscle
and sensory innervation of a posterolateral area of the scrotum in the
male. It mediates sensory innervation of a small posterolateral area of
the labia majora in the female. The ilioinguinal nerve (Ll) mediates
sensory innervation of a small anterolateral region of the scrotum or labia
2. There is also
parasympathetic and sympathetic innervation passing to vasculature, erectile
tissue, and glands in this region. The parasympathetic and sympathetic
nerves travel with blood vessels and branches of the pudendal nerve supplying
Figure 38. Schematic drawing showing
the course of the pudendal nerve in the male (pseudoparasagittal view).
The trajectory of the nerve is similar in the female, except that branches
pass to the labia majora and clitoris, rather than scrotum and penis. (Modified
from: Snell, Clinical Anatomy for Medical Students, Fig. 6, p. 326.)
3. The major arterial
blood supply and venous drainage of the perineum is by way of branches
of the internal pudendal artery and vein. The internal pudendal artery
and vein follow a trajectory similar to that described for the pudendal
nerve (see Fig. 38 above).
Exception to rule 3: The anteromedial
regions of the scrotum and labia majora receive some of their vascular
supply from deep and superficial external pudendal arteries, which are
branches of the femoral artery.
4 The lymphatic
drainage of the perineum is mainly to superficial inguinal nodes.
5. The urogenital
triangle can be further subdivided into inferior and superior portions
by the existence of a musculofascial diaphragm called the urogenital
diaphragm. This bears some explaining: Think of the pelvic cavity as
a two story building. The upper story is the pelvic cavity proper, the
lower story is the perineum.
The pelvic diaphragm, which forms the
floor of the pelvic cavity proper, therefore forms the ceiling or roof
of the perineum. The perineum can be subdivided into an anal triangle and
a urogenital triangle, as describer} above. Imagine now that the schematic
drawing below is a view of the pelvis from the side:
The urogenital diaphragm is like a mezzanine
or balcony in the first story of the two-story building, jutting out into
the space of the urogenital triangle, but not into the anal triangle. The
urogenital diaphragm fills in the area between the pubic rams, dividing
the urogenital triangle into a part inferior to the diaphragm, called the
superficial pouch, a space between the fascial sheets forming the
diaphragm, called the deep pouch, and a space between the pelvic
diaphragm and the urogenital diaphragm, which is not usually given a special
The urogenital diaphragm consists of
3 layers: an inferior layer of fascia, known as the perineal membrane;
a muscle laver, containing the sphincter urethrae (which acts
as a voluntary sphincter for the urethra) and deep transverse perineal
muscles; and a superior layer of fascia. The muscle layer is "sandwiched"
between the two fascial sheets, which fuse anteriorly and posteriorly.
(See Fig. 43 below for a further explanation of the urogenital diaphragm.)
Posteriorly, the fascial sheets and the insertions of the deep transverse
perineal muscles fuse at the perineal body. As pointed out above,
the space between the inferior and superior fascia of the urogenital diaphragm
comprises the deep perineal pouch.
The anal triangle
Figure 39. Drawing showing the arrangement
of the puborectalis muscle, and the deep, superficial, and subcutaneous
portions of the external anal sphincter. (From: Snell, Clinical Anatomy
for Medical Students. Fig. 7, p. 324.)
As stated above, the major structure
of the anal triangle is the anal canal. The anal canal contains
an internal sphincter of smooth muscle within its walls, which is involuntary.
Around the anal canal, on its external surface, passes the external
anal sphincter, which is a striated muscle, and therefore under voluntary
control. The disposition of the subcutaneous, superficial and deep portions
of the external anal sphincter is summarized in Fig. 39. Note that the
puborectalis portion of the levator ani forms a "sling" around the rectum,
which helps to maintain fecal continence.
Figure 40. Diagram illustrating the
puborectalis sling, which forms an angle in the rectum between the anal
canal and rectum, helping to maintain fecal continence. (From: Grant's
Atlas, Fig. 3-40.)
The nerve supply to the external
anal sphincter is by way of inferior rectal nerves, which are branches
of the pudendal nerve (see Fig. 38). The blood supply to the upper part
of the anal canal is from branches of the superior rectal artery, which
continue from the pelvic cavity. Lymphatic and venous drainage parallel
the arterial blood supply. The blood supply to the lower part of the anal
canal is from inferior rectal arteries and veins, which are branches of
the internal pudendal artery and vein. Lymphatic drainage is to the superficial
There is a wedge-shaped space on
either side of the anal canal which is bounded superomedially by the pelvic
diaphragm, laterally by the obturator internus, and inferiorly by the skin.
This space is known as the ischiorectal fossa. In life this space
is filled with fat, which is almost liquid at body temperature and allows
for easy distension of the anal canal during defecation (see Fig. 41).
Figure 41. Frontal section through the
ischiorectal fossa, showing the disposition of the anal canal, external
anal sphincter, and the boundaries of the ischiorectal fossa. (From: Basmajian,
Grant's Method of Anatomy, Fig. 16.5, p. 199.)
The urogenital triangle
Figure 42. Columns of erectile tissue
forming the root and body of the penis in the male, and comprising the
crura of the clitoris and bulb of the vestibule in the female. (From: O'Rahilly,
Basic Human Anatomy, Fig. 38-4, p.313.)
The externally visible structures
of the urogenital triangle have been illustrated in Figs. 36 and 37. In
the male these are the penis and scrotum; in the female these include the
labia majora, labia minora, clitoris, and urethral and vaginal orifices.
Immediately beneath the skin of the urogenital triangle is a layer of membranous
fascia, which is continuous with the superficial membranous fascia of the
abdomen. The membranous fascia fuses with the superficial fascia of the
urogenital diaphragm (perineal membrane) at its posterior border.
Deep to the superficial membranous
fascia, and lying between it and the perineal membrane, is the superficial
pouch. The major contents of the superficial pouch are columns of erectile
tissue and thin sheets of muscle covering the erectile tissue and the posterior
portion of the perineal membrane, nerves supplying these muscles and the
overlying skin (perineal branches of the pudendal nerve), and blood
vessels supplying the region (branches of internal pudendal vessels). Figure
42 shows the disposition of the erectile tissue in the superficial pouch
in males and females.
In the male, three columns of erectile
tissue comprise the root of the penis: the two crura and the bulb of the
penis. The anterior continuations of these columns of erectile tissue,
the (2) corpora cavernosa and the corpus spongiosum, fuse to form the body
of the penis. The expanded continuation of the corpus spongiosum forms
the glans of the penis. Realize that the penile portion of the urethra
runs through the corpus spongiosum to its orifice in the glans.
In the female, there are four columns
of erectile tissue in the superficial pouch: two crura of the clitoris,
which fuse anteriorly to form the clitoris; and the two bulbs of the vestibule.
The columns of erectile tissue in
both male and female are covered over by thin sheets of muscle. The crura
of the clitoris and penis are covered by the ischiocavernosus muscle;
while the bulb of the penis and bulbs of the vestibule are covered by the
bulbospongiosus muscle. A thin strip of muscle also covers the posterior
portion of the perineal membrane: this is called the superficial transverse
perineal muscle (summarized in Fig. 43 e and f).
In the female, the greater vestibular
glands also sit in the superficial pouch just posterior to the bulbs of
the vestibule. Their ducts open onto the mucous membrane between the hymen
and the labia minora. The fluid secreted by these glands performs a lubricating
function during sexual arousal.
The urogenital diaphragm has been
described above. Figure 43 b-d illustrates the layers of the urogenital
diaphragm, and the disposition of the sphincter urethrae and deep transverse
perineal muscles in the deep perineal pouch. Realize that the urethra passes
through the urogenital diaphragm in both male and female. In the male,
the portion of the urethra located within the deep perineal pouch is known
as the membranous urethra.
The contents of the deep perineal
pouch in the male also include the bulbourethral glands which
produce a lubricating fluid. Note, however,
that the ducts of these glands open into the urethra in the superficial
pouch. just below the perineal membrane.
The vagina also passes through the
deep perineal pouch in the female.
In both sexes the contents of the
deep pouch also include blood vessels and nerves supplying this region.
These are branches of the pudendal nerve and internal pudendal vessels.
Figure 43. Schematic diagrams summarizing
the contents of the urogenital triangle in male and female. Note that level
F is the most superficial, A is the deepest. (From: Moore, Clinically Oriented
Anatomy, Fig. 3-16, p. 309.)
Part 2. Directions for carrying
out the dissection of pelvis and perineum.
Begin by tracing the inferior continuation
of the peritoneal sac from the abdomen into the pelvis.
In the male, note the relationship
of the peritoneum to the bladder, ureters, and rectum (see Fig. 24). Locate
the rectovesicle pouch between the bladder and the rectum. This
is the lowest portion of the peritoneal cavity in the male (in the upright
position). Gently strip off the peritoneum to expose the underlying structures.
If you have enough visibility, identify
the bladder, rectum, prostate, and puboprostatic ligaments at this time.
Sever the puboprostatic ligaments on the right side. Attempt to identify
the muscles forming the floor and walls of the pelvic cavity proper (Atlas
Fig. 3-12). Sever the attachment of the levator ani muscle to the obturator
internus muscle on the right side only (see Fig. 15).
In the female, note the relation
ship of the peritoneum to the bladder, uterus, and rectum (see Fig. 24).
Locate the vesicouterine pouch between the bladder and the uterus,
and the rectouterine pouch between the uterus and the rectum. The
rectouterine pouch is the lowest portion of the peritoneal cavity in the
female (in the upright position). Identify the components of the broad
ligament (see Figs. 33 and 34). Attempt to leave the broad ligament intact
on the right side, but strip off the remainder of the peritoneum to expose
the underlying structures.
If you have enough visibility, identify
the bladder, rectum, uterus, uterine tubes, and ovary at this time. Try
to identify the pubocervical, transverse cervical, and sacrocervical ligaments
(see Fig. 32). Sever these ligaments on the right side. Attempt to identify
the muscles forming the floor and walls of the pelvic cavity proper (Atlas
Fig. 3-13). Sever the attachment of the levator ani muscle to the obturator
internus fascia on the right side only (Fig. 15).
You will have much better access
to the structures of the pelvic cavity proper and perineum if you can widen
the pelvic inlet and spread the legs of the cadaver. This is accomplished
by "disarticulating" the pelvis. The next few paragraphs and figures will
tell you how to accomplish this operation.
1. If this hasn't
already been done, remove the skin from the front of the symphysis pubis.
Do not skin the external genitalia at this time. Palpate and sever the
suspensory ligament of the penis or clitoris. By blunt dissection,
using the handle of your scalpel or forceps, detach all of the soft tissue
structures from the inferior border of the symphysis pubis. With a scalpel
blade, cut through the symphysis pubis, avoiding the urinary bladder. BE
CAREFUL that the blade does not pop off of your scalpel handle during this
operation and cut you. Clean the front of the pubic bone on the right side
to about 4 cm. from the midline. With a saw, make a cut through the pubis
roughly 3 cm. from the midline and remove the wedge of bone (see Fig. 44
below). Again, take care not to cut into the soft tissues of the pelvic
Figure 44. Drawing indicating the approximate
position of cuts to be made through the symphysis pubis and pubic bone.
2. Turn the cadaver
to the prone (face down) position. Make skin incisions as shown below to
expose the gluteal region (see Fig. 45). Remove skin and superficial fat
in the region of the buttocks, skin only over the posterior thigh.
Figure 45. Diagram indicating the skin
incisions which should be made to expose the gluteal region. (From: Grant's
Dissector, Fig. 3.15, p. 56.)
This will expose the gluteus maximus
muscles (see Fig. 46).
Figure 46. Diagram the disposition of
the gluteus maximus muscle on the Eight side. (From: Grant's Atlas, Fig.
Clean and expose the superior, medial,
and inferior borders of the gluteus maximus on both sides. On both sides.
detach the upper medial border from the ilium. Then detach the medial portion
from the sacrum and coccyx. Palpate the medial part of the inferior border
of the gluteus maximus. Note that it is attached to the sacrotuberous ligament.
Carefully detach the gluteus maximus from the sacrotuberous ligament. Do
not cut the sacrotuberous ligament at this time. Reflect the gluteus maximus
muscle laterally to the point where the inferior gluteal vessels enter
it. Try not to sever the inferior gluteal nerves and vessels. Remember,
the goal at this moment is not to do a complete dissection of the
gluteal region (this will be done in a later dissection). Your goal here
is to gain sufficient exposure of structures of the pelvis and perineum
and to be able to disarticulate the pelvis.
Identify the sacrospinous and sacrotuberous
ligaments and the greater and lesser sciatic foramina on both sides. Locate
the internal pudendal vessels and pudendal nerve as they leave the pelvis
through the greater sciatic foremen, loop around the sacrospinous ligament,
and enter the perineum through the lesser sciatic foremen (see Fig. 23).
ON THE RIGHT SIDE ONLY, cut the sacrotuberous
ligament close to the ischial tuberosity; cut the sacrospinous ligament
close to the ischial spine (see Fig. 47 below). DO NOT CUT THE PUDENDAL
NERVE AND VESSELS
Figure 47. Draining showing where the
sacrotuberous and sacrospinous ligaments should be cut.
3. Return the
cadaver to the supine position. Place a block under the small of the back.
Check to see that the psoas muscle has been removed on the right
side in the course of the previous dissection. (If the right psoas has
not been removed, check with your instructor as to the best way to accomplish
this.) You are non ready to disarticulate the pelvis. Your goal is to break
apart the right sacroiliac joint by abducting the lower limbs. Force the
feet of the cadaver up to 1 meter apart. As you do this you should hear
the noise caused by the tearing of the sacroiliac ligaments. Keep the lower
limbs abducted using a wooden block between the legs, or use ropes to tie
the limbs in an abducted position. Palpate the region of the right sacroiliac
joint to see if there a gap there. If you have been unable to disarticulate
the joint, seek the assistance of an instructor.
Now that you have widened the access
to the pelvis, complete your exploration of the pelvic cavity proper Trace
the elements of the urinary and gastrointestinal systems from the abdomen
to the pelvic cavity. Trace the course of the male or female reproductive
tracts (see Figs. 27 and 28). Identify the vasculature supplying these
organ systems. Identify the fascial supports of the prostate and the uterus
(Fig. 32). Identify the muscles forming the walls end floor of the pelvic
cavity (Figs. 12-16,Atlas Figs. 3- 1 2, 3- 13). Trace the sources of arterial
blood supply to the pelvic cavity, including the major branches of the
internal iliac artery (see Figs. 20 and 30). Follow the sympathetic trunk
from the abdomen to sacral levels. Trace some of the branches of the hypogastric
plexus if they are readily visible. Do not spend time on this if
the hypogastric plexus is not readily visible (Fig. 22). Trace the obturator
nerve from its origin at L2-4 in the abdomen into the pelvis and through
the obturator foremen (see Fig. 15). Locate the contributions from L4 and
5 which form the lumbosacral trunk, crossing the pelvic brim to join with
contributions from S 1-3 to form the sciatic nerve. Trace the sciatic nerve
to where it exits the pelvis through the greater sciatic foremen. Note
the formation of the pudendal nerve from S2-4. Trace this nerve as it leaves
the pelvic cavity through the greater sciatic foremen together with the
internal pudendal vessels (see Fig. 22).
Now turn your attention to dissection
of the perineum:
In the male, remove the skin from
the scrotum, penis, and anal region out to the boundaries of the pelvic
In the female, skin the entire perineum
except for the mucous membrane enclosed by the labia Sonora. Cut the edges
of the labia minora so that you have roughly 1/4 inch of labia minora left,
forming a rim around the mucous membrane.
When you have finished skinning,
turn your attention to the anal triangle. This can be dissected with the
cadaver in either the prone or supine position, whichever you find more
convenient. By blunt dissection, shell the fat out of the ischiorectal
fossa. Your goal is to expose the inferior rectal nerves and vessels passing
to the anal canal (see atlas Fig. 3-17). Trace these nerves beck to their
origin from the pudendal nerve and internal pudendal vessels. Trace pudendal
nerves and vessels through the pudendal canal. in the wall of the ischiorectal
fossa (see Fig. 38). Clean and identify the external anal sphincters.
Now turn your attention to the urogenital
triangle. Clean any remaining fat from the region. Using Fig. 43 as a guide,
attempt to identify the structures of the male and female urogenital triangle.
Remember, the muscles of this region are usually very thin, so dissect
cautiously. Erectile tissue has a characteristic reddish spongy appearance
and should be easy to identify.
If you have a male cadaver, dissect
the penis to identify the paired dorsal arteries and nerves, which are
branches of the internal pudendal artery and pudendal nerve, respectively.
Identify the single deep dorsal vein of the penis and attempt to trace
it back to where it drains into the prostatic venous plexus. Verify
that the paired corpora cavernosa pass on the dorsum of the penis (nearest
the abdomen), while the corpus spongiosum passes on the ventral side of
the penis (nearest the lower limb). Verify that the urethra passes through
the corpus spongiosum and opens to the outside world through an orifice
in the glans, which is the expanded end of the corpus spongiosum. Use Fig.
48 as a guide for your dissection. It is not necessary to transect the
Figure 48. Dissection of the penis.
(From: Grant's Dissector, Fig. 3.19, p. 59.)
When you have completed the dissection,
review your work by running through the anatomy, function, and nerve and
vascular supply of the reproductive system and the pelvic portions of the
gastointestinal and urinary systems.