Transcript Dissection of Intercostal Spaces

Dissection of
Intercostal Spaces
Clean the external intercostal muscle
and note that its fibers are directed
downward and forward from the
inferior border of the rib above to the
superior border of the rib below.
Follow the muscle anteriorly to where
it is continuous with an aponeurosis
called the anterior intercostal
membrance.
Remove the anterior intercostal membrance
to expose the underlying portion of the
internal intercostal muscle between the
costochondral junction and sternum. Note
that the fibers of the internal intercostal
muscle are directed at right angles to the
external intercostal fibers and pass
downward and backward from the
superior border of the rib below.
The muscle extends backward
from the sternum to the angles of
the ribs posteriorly, where the
muscle is replaced by an
aponeurosis, the posterior
intercostal membrance.
Identify the lateral cutaneous branch of the fifth
intercostal nerve and follow it under the lower
margin of the fifth rib to the fifth intercostal nerve.
Carefully cut the internal intercostal muscle from
the sixth rib and turn it upward. Identify again the
fifth intercostal nerve and follow it anteriorly and
posteriorly, noting its relationship to the rib and
corresponding artery and vein.
The transversus
thoracis muscle
forms the deepest layer of the
intercostal muscles; it is vestigial and
corresponds
to
the
transversus
abdominis muscle in the anterior
abdominal wall. The transversus
thoracis muscle will be dissected
later on the inside of the thorax.
Repeat the above dissection in the
eighth intercostal space and note
how the eighth intercostal nerve
leaves the thoracic wall to enter
the anterior abdominal wall by
passing deep to the ninth costal
cartilage.
Cut through the parietal pleura
in
the
fourth
and
eighth
intercostal spaces and note that
you have entered the pleural
cavity. Observe the underlying
collapsed lung covered with
visceral pleura.
Take a sharp, pointed probe and
pierce an adjacent intercostal
space. Picture in your mind the
various layers of tissue that the
probe passes through before it
enters the pleural cavity. This
exercise is of great clinical value.
Dissection of
Pleurae
Enter the thoracic cavity by cutting
through on both sides the costal
cartilages from the xiphisternal joint
to the midaxillary line two figers
breadth above and curving parallel
with the costal margin. Be careful not
to enter the abdomen by cutting
through the diaphragm.
Continue the incision through the ribs
with bone gorceps or bone cutting saw,
superiorly along the midaxillary line. In
the case of the second and third ribs, cut
them as far posteriorly as possible
without damaging the contents of the
axilla. Cut across the first rib lateral to
the origin of the subclavius muscle and
the clavicle near its center.
Divide the sternum at or near the
xiphisternal joint. Gently elevate the
inferior end of the body of the sternum
with the costal cartilages and the
anterior parts of the ribs. Identify the
costal parietal pleura and note how it is
reflected from the back of the sternum
onto the mediastinum on both sides.
Divide the parietal pleura where it leaves
the sternum and lift the anterior wall of
the thorax upward, leaving it hinged at the
root of the neck by the cervical fascia and
attached neck muscles. Note the smooth
parietal pleura on the posterior surface of
the anterior thoracic wall.
Now strip the pleura from the back of
the sternum and costal cartilages and
expose the transversus thoracis muscle
and the internal thoracic vessels and
their branches. Clean the internal
thoracic vessels and note the terminal
division of the internal thoracic artery
in the sixth intercostal space into the
superior epigastric and musculophrenic
arteries.
The trasversus thoracis muscle forms the
deepest layer of the intercostal muscles
and corresponds to the transversus
abdominis muscle in the anterior
abdominal wall. It may be divides into
three portions, which are more or less
separate from one another: (1) the
subcostalis, (2) the intercostalis intimus,
and (3) the sternocostalis.
The internal thoracic artery is a branch
of the first part of the subclavian artery
in the neck. It descends vertically on
the pleura posterior to the costal
cartilages, a fingerbranch lateral to the
sternum, and ends in the sixth
intercostal space by dividing into the
superior epigastric and musculophrenic
arteries.
Now that the pleural cavity has been opened, it
is possible to pass the hand around the
collapsed lung, except where the visceral pleura
becomes continuous with the mediastinal
parietal pleura at the lung root. Carefully
explore the extent of the pleural cavity and
realize that in the living, with the lung
expanded, the visceral and parietal layers of
pleura are in apposition, separated by only a
thin film of pleural fluid.
Identify the various parts of the parietal
pleura, costal, diaphragmatic, mediastinal,
and cervical. Place your fingers in the
right and left costodiaphragmatic recesses.
Identify the root of the lung and the
pulmonary ligament.
Dissection of Lungs
Identify the cardiac notch of
the left lung. Retract the
lungs laterally to expose the
mediastinal pleura over the
fibrous pericardium.
Study the root of the lung but do
not cut into it yet. Verify that at
the lung root the visceral pleura
covering
the
lung
becomes
continuous with the mediastinal
parietal pleura.
Push the lung laterally and
stretch the root of the lung.
Now divide the root with a
scalpel and remove the
lung. Repeat the process on
the opposite side.
Study the surfaces and borders of
each lung. The surfaces are costal,
medial, and basal, and the borders
are thin and are anterior and inferior.
The apex of the lung projects
superiorly into the root of the neck.
Compare the right and left lungs.
Identify the structures in the lung root
and follow them into the substance of the
lung for a short distance. Examine the
bronchus, pulmonary artery,
and
pulmonary vein,The bronchus is situated
posteriorly, the pulmonary artery
superiorly, and the pulmonary veins
inferiorly. The right upper bronchus is
different in that it lies superior to the
pulmonary artery.