Dissection of Anterior Abdominal Wall

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Dissection of Anterior Abdominal Wall
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With the cadaver in the supine position, incise
the skin in the midline from the xiphisternal
joint to the pubic symphysis, cutting around the
umbilicus. Then incise the skin 1 inch above the
pubis symphysis laterally over to and a little
above the iliac crest to the midaxillary line on
both sides. Reflect the skin from the midline
anteriorlly to the midaxillary line, leaving the
superficial fascia on the anterior abdominal wall.
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Identify the fatty layer of the superficial
fascia ( Camper's fascia)and note that it is
continuous below with the fatty superficial
fascia of the thigh and above with the
superficial fascia of the thorax. Note that the
fat is greatest in amount over the inferior half
of the abdomen.
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Note also the terminal portion of the superficial
arteries and cutaneous nerves in this layer also
observe the superficial veins.
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Identify the Membranous Layer of the Superficial
Fascia (Scarpa's Fascia). Note That It Lies Deep
to the Fatty Layer and Immediately Superficial
to the aponeurosis of the External Oblique
Muscle. Insert a Finger Between the Membranous
Layer and the aponeurosis of the External Oblique
and Separate Them Inferiorly.
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Note That the Finger Can Be Passed Down Medial to
the Pubic Tubercle Along the Spermatic Cord and
Anterior to the Body of the Pubis Into the
Perineum.Lateral to the Pubic Tubercle the Finger
Cannot Enter the Thigh, However,since the
Membranous Layer Is Attached to the Deep Fascia
of the Thigh Just Below the Inguinal Ligament.
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Identify the Superficial Inguinal Ring Above the
Pubic Tubercle but Do Not Disturb It at This
Stage. The Ring Is a Triangular Opening in the
aponeurosis of the External Oblique Muscle.
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Make a vertical incising through the full
thichness of the superficial fascia from the
xiphoid process to the symphysis pubis. With the
aid of a scalpel handle, carefully reflect the
flaps of fascia laterally, separating the fascia
from the aponeurosis of the external oblique
muscle.
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Identify examples of anterior and lateral
cutaneous nerves. Remove all the flaps of
superficial fascia by making a vertical incision
through the fascia in the midaxillary line.
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External oblique muscle. Clean the surface of
the external oblique muscle and its aponeurosis.
Note the attachment of the fleshy origin from
each of the lower eight ribs. Here it
interdigitates with the origin of the serratus
anterior and the latissimus dorsi.
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Observe the direction of the muscle fibers.
Identify the linea alba that extends from the
xiphoid process down to the symphysis pubis and
is formed by the fusion of the aponeurosis of the
muscle of the two sides.
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Carefully define the margins of the superficial
inguinal ring lying above the pubic tubercle.
Note that it is triangular in shape and not
round. In the male, identify the spermatic cord
emerging from this aperture and confirm that its
outer covering, the external spermatic fascia, is
attached to the margins of the ring.
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In the female, the round ligament of the uterus
emerges from the ring. Again confirm that its
outer covering is attached to the margin of the
ring. Identify the ilioinguinal nerve as it
emerges from the lateral part of the superficial
inguinal ring.
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Identify the inguinal ligament and note that it
is formed by the lower margin of the aponeurosis
of the external oblique muscle. The ligament is
attached laterally to the anterior superior iliac
spine and medially to the pubic tubercle.
Attached to the lower margin of the ligament is
the deep fascia.
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Internal Oblique Muscle. Free the
interdigitating origins of the external oblique
muscle from those of the serratus anterior as far
as the midaxillary line. Incise the external
oblique down the midaxillary line to the iliac
crest. Now find the plane between the external
oblique and the internal oblique muscles. With
the fingers, free the external oblique from the
internal oblique and gradually turn the upper
part of the external oblique forward.
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Note that the fibers of the internal oblique
muscle run downward and backward, that is, at
right angles to the fibers of the external
oblique. Continue to reflect the external oblique
forward and medially toward the lateral margin of
the rectus sheath to fully expose the underlying
internal oblique muscle. Study the origins and
insertions of the external oblique and its
innervation.
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Make a vertical incision through the aponeurosis
of the external oblique muscle 1 inch lateral to
the rectus sheath and extend it down to a point 3
inches above the pubic tubercle. Turn the
inferior portion of the external oblique downward
and carefully examine the superior surface of the
inguinal ligament.
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It is most important that you understand the
attachments and configuration of the inguinal
ligament. Note that the ligament is the inrolled
lower margin of the aponeurosis of the external
oblique and confirm again that it is attached to
the pubic tubercle medially and the anterior
superior iliac spine laterally.
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Carefully follow the inguinal ligament medially
to the pubic tubercle, follow the fibers backward
as the lacunar ligament, and note the attachment
to the pectineal line. Note the continuity of the
lacunar ligament with the pectineal ligament.
Study the relationship of the inguinal, lacunar,
and pectineal ligaments to the femoral sheath.
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Clean the surface of the internal oblique muscle.
Define the inferior border of the muscle and note
its relationship to the spermatic cord or round
ligament of the uterus. Study closely the origin
of the internal oblique from the inguinal
ligament. Note that the internal oblique fibers
arise from the lateral half of the ligament and
therefore lie anterior to the deep inguinal ring.
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Identify the cremaster muscle passing onto the
spermatic cord from the lower edge of the
internal oblique muscle. Clean the ilioinguinal
nerve and follow it proximally to where it
emerges from the internal oblique muscle.
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Exposure of transversus abdominis muscle. Cut
through the attachments of the internal oblique
muscle to the costal margin and transect it
vertically along the midaxillary line. Cut
through the origin from the iliac crest and the
inguinal ligament.
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Insert your fingers into the plane between the
internal oblique and underlying transversus
abdominis muscle. Reflect the internal oblique
muscle forward to the lateral margin of the
rectus sheath to expose fully the underlying
transversus abdominis muscle and the intercostal
neres.
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At the lateral edge of the rectus abdominis, the
aponeurosis of the internal oblique is seen to
split and pass anterior and posterior to the
rectus abdominis the anterior layer fuses with
the aponeurosis of the external oblique muscle,
and posterior layer fuses with that of the
transversus abdominis. This aponeurotic covering
to the rectus abdominis is called the rectus
sheath.
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Transversus abdominis muscle. Clean the surface
of the transversus abdominis and the vessels and
nerves that lie on it. Note that the fibers of
the transversus muscle run in a horizontal
direction. Identify the lower margins of the
transversus abdominis muscle and follow its
fibers medially to join with those of the
internal oblique to form the conjoint tendon.
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Examine the attachment of the conjoint tendon to
pubic crest and the pectineal line. Note that the
conjoint tendon lies immediately posterior to the
superficial inguinal ring. Again examine the
inguinal, lacunar, and pectineal ligaments and
note their relationship to the conjoint tendon.
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Fascia transversalis. Insert the handle of the
scalpel between the lower margin of the
transversus abdominis muscle and the underlying
fascia transversalis. Remember that this fascia
lines the abdominal wall and forms the posterior
wall of the inguinal canal lateral to the
conjoint tendon.
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The fascia transversalis is tissue-paper thin,
and the extraperitoneal fat can be seen through
it. Deep to the fat is the peritoneal lining of
the abdominal cavity.
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Rectus Sheath. The rectus sheath is a long
sheath that encloses the rectus abdominis muscle
and pyramidalis muscle (if present) and contains
the anterior rami of the lower six thoracic
nerves and the superior and inferior epigastric
vessels and lymphatics. It is formed largely by
the aponeurosis of the three anterolateral
abdominal muscles.
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Open the entire length of the rectus sheath by a
longitudinal incision just lateral to the linea
alba. Identify the medial edge of the rectus
abdominis muscle. Raise its medial edge and, with
the finger or blunt end of the forceps, verify
that it is possible to separate the rectus muscle
from the posterior layer of the sheath.
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Note and preserve the nerves and vessels passing
through the posterior wall of the sheath into the
lateral part of the muscle.
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Reflect the lateral part of the anterior layer of
the sheath by cutting free the attached tendinous
intersections of the rectus muscle. Examine again
the linea alba and realize that it is formed by
the fusion of the aponeuroses of the three
lateral muscles of the abdominal wall on the two
sides. It extends from the xiphoid process down
to the sympgysis pubis and separates the rectus
abdominis muscles on the two sides.
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Understand What Is Meant by the Term linea
semilunaris. This Is a Curved Ridge Formed by the
Lateral Margin of the rectus abdominis Muscle.
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Clean the rectus abdominis and Identify the
pyramidalis Muscle if Present. Transect the
rectus Muscle at Its Middle and Raise the Upper
and Lower Ends, Cutting the Nerves That Enter It.
Identify the Superior epigastric Artery That
Enters the rectus Sheath by Emerging From Beneath
the Lower Margin of the Seventh Costal Cartilage
and Passing Down Posterior to the rectus Muscle.
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Note also the inferior epigastric artery that
ascends within the sheath from below. Verify the
origin and insertion of the rectus abdominis and
the pyramidalis muscles. Finally,remove both of
these muscles.
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Carefylly examine the anterior and osterior walls
of the rectus sheath and verify their formation
from the aponeuroses of the anterior abdominal
muscles. Note that the posterior wall ends below
at the arcuate line, where the aponeuroses of the
internal oblique and trasversus abdominis muscles
pass anterior to the rectus muscle.
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Cut free the attachments of the internal oblique
and trasversus abdominis muscles from the costal
margin. Incise the latter muscle along the
midaxillary line to the iliac crest. Try to
preserve the underlying peritoneum intact.
Reflect all the abdominal muscles and the fascia
transversalis inferiorly as a unit by blunt
dissection. Cut around the umbilicus to preserve
its connection with the ligamentum teres of the
liver.
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Deep inguinal ring. Before destroying the fascia
transversalis in the inguinal region, pull on the
spermatic cord or round ligament of the uterus
from the anterior surface and identify the deep
inguinal ring and the internal spermatic fascia.
Confirm that the deep ring lies lateral to the
inferior epigastric vessels.
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The Abdominal Cavity
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Peritoneum. The peritoneum is a serous membrane
lining the walls of the abdominal cavity and
clothing the abdominal viscera. The parietal
peritoneum lines the walls of the abdominal
cavity, and the visceral peritoneum covers the
abdominal organs.
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The peritoneum secretes a small amount of serous
fluid, which lubricates the surfaces of the
peritoneum and facilitates free movement between
the viscera. The potential space between the
parietal and visceral layers of the peritoneum is
called the peritoneal cavity.
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The peritoneum has the following important
arrangements 1. The peritoneal cavity is
divided into the greater and the lesser sac. The
greater sac is the main compartment, and it
extends across the whole breadth of the abdomen
and from the diaphragm to the pelvis. The lesser
sac is the smaller compartment, and it lies
behind the stomach, as a diverticulum from the
greater sac it opens through an oval window
called the opening of the lesser sac, or the
epiploic foramen.
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2. A mesentery is a two-layered fold of
peritoneum that attaches part of the intestines
to the posterior abdominal wall, and it includs
the mesentery of the small intestine, the
transvers mesocolon, and the sigmoid mesocolon.
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3. An omentum is a two-layered fold of peritoneum
that attaches the stomach to another viscus. The
greater omentum is attaches to the greater
curvature of the stomach, and it hangs down like
an apron in the space between the coils of small
intestine and the anterior abdominal wall.
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It is folded back on itself and is attached to
the inferiorborder of the transverse colon. The
lesser omentum slings the lesser curvature of the
stomach to the undersurface of the liver. The
gastrosplenic omentum (ligament) connects the
stomach to the spleen.
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4. The peritoneal ligaments are two-layered folds
of peritoneum that attach the less mobile solid
viscera to the abdominal walls. The liver, for
example, is attached by the falciform ligament to
the anterior abdominal wall and to the
undersurface of the diaphragm. The mesenteries,
omenta, and peritoneal ligaments allow blood
vessels, lymphatics, and nerves to reach the
various viscera.
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Opening of Abdominal cavity and Inspection of Its
Contents.
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When the peritoneal cavity has been opened by
making a transverse incision through the parietal
peritoneum lining the anterior abdominal wall at
the level of the umbilicus, identify three folds
of peritoneum that converge on the umbilicus from
below. These cover the two lateral umbilical
ligaments and the median umbilical ligament.
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Below the level of the anterior superior iliac
spines, two additional folds may be recognized,
due to the underlying inferior epigastric
arteries.
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Examine the falciform ligament, which extends
from the umbilicus to the liver. Identify the
ligamentum teres in the free margin of the
falciform ligament. Cut the peritoneum along the
costal margin, except where the falciform
ligament of the liver is attached. Reflect the
remainder of the peritoneum inferiorly by cutting
it down the midaxillary line on each side.
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Study the abdominal viscera in situ. Note the
relative size, shape, and position of all the
abdominal organs in the undisturbed abdominal
cavity. It is important to avoid any dissection
at this stage.
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Be prepared to find pathological changes that may
have been responsible for the person's death or
that may be evidence of previous disease. For
example, the peritoneum may be studded by
numerous secondary carcinomatous deposits that
have spread from a primary lesion in one of the
abdominal organs.
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Identify the following structures
1. The liver,
which is divided into right and left lobes by the
falciform ligament.2. The fundus of the
gallbladder, which projects beneath the lower
margin of the liver.

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3. The stomach, which lies in the epigastrium. It
is connected to the liver by the lesser
omentum.4. The greater omentum, which contains a
large quantity of fat. Free up the greater
omentum and reflect it superiorly to expose the
transverse colon.
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5. The spleen, which lies in the left
hypochondrium behind the stomach and in contact
with the diaphragm.6. The coils of small
intestine. Pull the greater omentum upward over
the costal margin and identify the coils of
jejunum in the upper left part of the abdominal
cavity and the coils of ileum in the lower right
part of the cavity.
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7. The large intestine. The cecum is a blind
pouch that lies below the level of the ileocolic
junction in the right iliac region. Identify the
appendix on its posteromedial surface. The cecum
is continuous above with the ascending colon,
then transverse colon, then descending colon and
sigmoid colon.
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