Dissection of the
Anterior
Compartment of the
Arm
Open the anterior of flexor
compartment of the arm by incising the
deep fascia in line with the previous
skin incisions. Reflect the fascia
laterally and medially. Expose the
long and short heads of the biceps
brachii, coracobrachialis, and
brachialis muscles.
Identify the brachial artery;
basilic
vein;musculocutaneous,
median, and ulnar nerves;
and the medial cutaneous
nerve of the forarm.
Comfirm that the biceps brachii muscle arises
by two heads. Note that the long head appears
to be shorter than the short head, since it
arises from the supraglenoid tubercle of the
scapula within the shoulder joint and emerges
from the joint beneath the transverse humeral
ligment. The short head arises from the tip
of the coracoid process of the scapula. Trace
the muscle belly down to its tendon in the
cubital fossa.
Clean the coracobrachialis muscle
from its origin on the tip of the
coracoid process of the scapula to
its insertion into the medial side of
the shaft of the humerus. Note that
the muscle is supplied and later
pierced by the musculocutaneous nerve.
Clean the brachialis muscle
and study its origin from the
anterior surface of the shaft
of the humerus. It is
inserted into the coranoid
process of the ulna in the
cubital fossa.
Brachial Artery.
This is a continuation of the
axillary artery at lower
border of the teres major
muscle. In the cubital fossa
it bifurcates into the ulnar
and radial arteries.
Clean the brachial artery and note
that it is crossed about halfway
down the arm by the median nerve
and is overlapped on the lateral
side by the biceps brachii muscle.
It may be easily palpated on the
medial side of this muscle in the
living. Identify the following
branches
1. Muscular branches to the
anterior compartment of the
upper arm.
2. Profunda brachii artery,
which arises near the
beginning of the brachial
artery and runs with the
radial nerve into the
posterior compartment of the
arm.
3. Superior ulnar collateral
artery, which arises near the
middle of the upper arm and
follows the ulnar nerve.
4. Inferior ulnar collateral
artery, which arises near the
termination of the artery and
takes part in the anastomosis
around the elbow joint.
5. Nutrient artery to the
humerus, which enters the
shaft of the humerus near the
insertion of the
coracobrachialis muscle.
Basilic Vein.
Trace the basilic vein from
the front of the elbow to the
lower border of the teres
major muscle. Here, it joints
with the venae comitantes of
the brachial artery to form
the axillary vein.
Nerves
Musculocutaneous nerve.
Trace this nerve from its origin from the
lateral cord of the brachial plexus downward
through the coracobrachialis muscle. Follow it
between the biceps and brachialis muscle and
note that it pierces the deep fascia of the
arm just above the elbow at the lateral margin
of the biceps tendon. It now continues down
the forearm as the lateral cutaneous nerve of
the forearm. Identify the branches to the
coracobrachialis, biceps, and brachialis
muscle.
Median nerve.
Trace the median nerve from its origin in the
axilla from the medial and lateral cords of
the brachial plexus downward into the cubital
fossa. Note that it first runs on the lateral
side of the brachial artery; then, about
halfway down the arm crosses the artery and
continues downward on the medial side of the
brachial artery. The median nerve has no
branches in the upper arm.
Ulnar nerve.
Trace the ulnar nerve from the medial cord of
the brachial plexus downward on the medial side
of the brachial artery as far as the middle of
the arm. Note that here, at the insertion of
the coracobrachialis, the nerve pierces the
medial fascial septum and enters the posterior
compartment of the arm. The ulnar nerve has no
branches in the anterior compartment of the
upper arm.
Medial cutaneous nerve of the
forearm. This nerve should be followed
from the medial cord of the brachial
plexus down the arm on the medial side of
the brachial artery. The medial cuatneous
nerve of the forearm pierces the deep
fascia with the basilic vein and divides
into anterior and posterior branches.
Identify the radial nerve as it leaves the
axilla and enters the posterior
compartment of the arm. Identify it again
as it enters the anterior compartment just
above the lateral epicondyle of the
humerus. Comfirm the existence of the
medial and lateral intermuscular fascial
septa.
Dissection of
the cubital
fossa
Extend the vertical skin incision on the
anterior surface of the arm downward into
the cubital fossa. Here, make a transverse
incision across the front of the fossa
about 5 cm below the level of the medial
and lateral epicondyles. Reflect the skin
flaps medially and laterally and completely
expose
the
contents
of
the
anterior
compartment of the arm and the cubital
fossa.
Identify and preserve the cephalic and
basilic veins. Study the arrangement of
the superficial veins lying anterior to
the cubital fossa; they are important.
Note that the cubital fossa lies in
front of the elbow joint and is
triangular in shape.
Confirm that it has the following
boundaries:
Laterally, the brachioradialis
muscle.
Medially, the pronator teres
muscle.
The base of the cubital fossa triangle
is formed by an imaginary line drawn
between the two epicondyles of the
humerus.
The floor of the fossa is formed by the
supinator muscle laterally and the
brachialis muscle medially.
The roof is formed by skin and fascia
and is reinforced by the bicipital
aponeurosis.
Identify and clean the
following structures
present within the cubital
fossa:
1. The median nerve runs
down on the medial side of
the brachial artery and
leaves the fossa by passing
between the two heads of
the pronator teres muscle.
2. The brachial artery
bifurcates into the
radial and ulnar
arteries.
3. The tendon of biceps brachii
passes to its insertion into the
bicipital tuberosity of the radius.
Note that the tendon gives off on
its medial side the bicipital
aponeurosis, which passes downward
and medially and fuses with the deep
fascia of the forearm.
4. Radial nerve.
Trace the radial nerve from the axilla
onto the long and medial heads of the
triceps and follow it to where it enters
the spiral groove on the posterior
surface of the humerus. Reidentify the
radial nerve as it returns to the
anterior compartment of the arm, above
the lateral epicondyle of the humerus.
Here, it lies between the brachialis and
the brachioradialis muscles.
Identify and clean the branches of the
radial nerve to the brachialis muscle,
brachioradialis muscle, and extensor
carpi radialis longus muscle. Identify
and clean the two terminal branches of
the radial nerve, namely, the deep
branch of the radial nerve, which
supplies the supinator muscle and then
pierces it, and the superficial branch
of the radial nerve, which leaves the
fossa by passing deep to the
branchioradialis muscle.
5. Lateral cutaneous nerve
of the forearm.
This nerve emerges from beneath
the lateral side of the biceps
brachii muscle and divides into
anterior and posterior branches,
which supply the skin of the
lateral side of the forearm.
Medial cutaneous nerve of
the forearm.
6.
This nerve runs down the medial side
of the brachial artery, pierces the
deep fascia about halfway down the
arm, and, in the region of cubital
fossa, divides into anterior and
posterior branches that supply the
skin of the medial side of the
forearm.
Dissection of the
posterior compartment
of the arm.
The posterior compartment of
the upper arm contains the
triceps muscle and its nerve
and blood supply. Passing
through the compartment are
the radial and ulnar nerves.
Make a vertical incision through the
deep fascia down the midline of the
posterior surface of the arm from the
deltoid muscle to the olecranon process
of the ulna. By means of transverse
incision at the upper and lower ends,
reflect medial and lateral flaps to
expose the underlying triceps brachii
muscle.
Clean the triceps muscle
and identify the lateral,
long, and medial heads.
Follow the muscle to its
insertion on the
olecranon process of the
ulna.
Radial nerve.
Expose the radial nerve and the
profunda brachii vessels by
dividing the lateral head of
triceps by means of an oblique
incision that runs downward and
laterally across the middle of
the arm.
Follow the nerve as it lies
within the spiral groove and
note that it pierces the
lateral intermuscular septum
to enter the front of the
arm.
Identify the
following branches of
the radial nerve:
1. Branches in the axilla.
Branches are given to long
and medial heads of the
triceps, and the posterior
cutaneous nerve of the arm
is given off.
2. Branches in the spiral groove. Branches
are given to the lateral and medial heads
of triceps. The lower lateral cutaneous
nerve of the arm supplies the skin over
the lateral and anterior aspects of the
lower part of the arm. The posterior
cutaneous nerve of the forearm runs down
the middle of the back of the forearm as
far as wrist.
3. Branches in the anterior compartment
of the arm. As noted previously, the
nerve after having pierced the lateral
fascial septum gives branches to the
brachialis, brachioradialis, and the
extensor carpi radialis longus muscles.
It also gives articular branches to the
elbow joint.
Ulnar nerve.
Identify the ulnar nerve as it pierces the
medial intermuscular septum at the level of
the insertion of the coracobrachialis muscle
to enter the posterior compartment of the
arm.. Follow the nerve and its accompanying
vessels downward posterior to the medial
epicondyle of the humerus. Note the important
relationship of the ulnar nerve to the medial
surface of the elbow joint.