The axilla is a pyramid-shaped space located between the upper arm and chest. It contains nerves, blood vessels, lymph nodes, and fat, and serves as an important passageway. The brachial plexus, formed from cervical and thoracic spinal nerve roots, passes through the axilla, branching into nerves that supply the upper limb. The axillary artery and its branches, including the thoracoacromial, lateral thoracic, and subscapular arteries, also course through the axilla, along with the axillary vein and lymph nodes.

1. The Axilla & Brachial
Plexus

2.  The axilla, or armpit, is a
pyramid-shaped space.
 It lies between the upper
part of the arm and the
side of the chest.
 It forms an important
passage for nerves, blood,
and lymph vessels as
they travel from the root
of the neck to the upper
limb.
 It consist of
 An apex
 Base
 Four walls

3.  The apex
 The apex, is directed into the root of
the neck.
 Apex is bounded:-
 In front by the clavicle
 Behind by the upper border of the
scapula
 Medially by the outer border of the
first rib.
 The base
 It is directed downwards.
 The base is formed by the skin
stretching between the anterior and
posterior walls
 It is bounded
 In front by the anterior axillary fold
(formed by the lower border of the
pectoralis major muscle),
 Behind by the posterior axillary fold
(formed by the tendon of latissimus
dorsi and the teres major muscle),
 Medially by the chest wall

4. Walls of the Axilla
 The walls of the axilla are
made up as follows:
 Anterior wall:
 By the pectoralis major,
subclavius, and pectoralis
minor muscles
 Posterior wall:
 By the subscapularis,
latissimus dorsi, and teres
major muscles from above
downwards.
 Medial wall:
 By the upper four or five ribs
and the intercostal spaces
covered by the serratus
anterior muscle
 Lateral wall:
 By the coracobrachialis and
biceps muscles in the bicipital
groove of the humerus.

7. Contents of axilla
 Axillary artery and its
branches
 Axillary vein and its
tributaries
 Infra clavicular part of
the Brachial Plexus & its
branches.
 Axillary lymph nodes &
the associated Lymph
vessels.
 The long thoracic &
intercosto brachial nerve.
 Axillary fat & areolar
tissue.

8. Axillary Artery
 It is as a continuation of the subclavian artery.
 The axillary artery begins at the lateral border of the 1st
rib and ends at the lower border of the teres major muscle,
where it continues as the brachial artery.
 Throughout its course, the artery is closely related to the
cords of the brachial plexus and their branches and is
enclosed with them in a connective tissue sheath called
the axillary sheath.
 If this sheath is traced upward into the root of the neck, it
is seen to be continuous with the prevertebral fascia.

9.  The pectoralis minor
muscle crosses in front
of the axillary artery
and divides it into
three parts.
 The first part is
proximal to pectoralis
minor.
 The second part is
posterior to pectoralis
minor.
 The third part is distal
to pectoralis minor.

11. First Part of the Axillary Artery
 This extends from the lateral border of the
1st rib to the upper border of the pectoralis
minor
Relations
 Anteriorly:
 The pectoralis major and the skin.
 The cephalic vein crosses the artery.
 Posteriorly:
 The long thoracic nerve (nerve to the
serratus anterior)
 Laterally:
 The three cords of the brachial plexus
 Medially:
 The axillary vein

12. Second Part of the Axillary Artery
 This lies behind the pectoralis
minor muscle.
Relations
 Anteriorly:
 The pectoralis minor, the pectoralis major,
and the skin
 Posteriorly:
 The posterior cord of the brachial plexus,
the subscapularis muscle, and the shoulder
joint
 Laterally:
 The lateral cord of the brachial plexus
 Medially:
 The medial cord of the brachial plexus and
the axillary vein.

14. Third Part of the Axillary Artery
This extends from the lower border of the pectoralis
minor to the lower border of the teres major
Relations
 Anteriorly:
 The pectoralis major for a short distance; lower down the
artery, it is crossed by the medial root of the median nerve.
 Posteriorly:
 The subscapularis, the latissimus dorsi, and the teres major.
 The axillary and radial nerves also lie behind the artery.
 Laterally:
 The coracobrachialis, the biceps, and the humerus.
 The lateral root of the median and the musculocutaneous
nerves also lies on the lateral side.
 Medially:
 The ulnar nerve, the axillary vein, and the medial cutaneous
nerve of the arm, the cephalic vein.

15. Branches of the Axillary Artery
 From the first part:
 The highest thoracic
artery is small and
runs along the upper
border of the pectoralis
minor.
 From the second part:
 The thoracoacromial
artery immediately
divides into terminal
branches.
 The lateral thoracic
artery runs along the
lower border of the
pectoralis minor.

17.  From the third part:
 The subscapular artery
runs along the lower
border of the
subscapularis muscle.
 The anterior and
posterior circumflex
humeral arteries wind
around the front and the
back of the surgical neck
of the humerus,
respectively.

18. Axillary Vein
 The axillary vein is formed at the lower
border of the teres major muscle by the
union of the venae comitantes of the
brachial artery and the basilic vein.
 It runs upward on the medial side of the
axillary artery and ends at the lateral
border of the 1st rib & becomes continues
as the subclavian vein.
 The vein receives tributaries, which
correspond to the branches of the axillary
artery.

20. The brachial plexus
 The brachial plexus is formed by the union of the ventral rami of
the lower four cervical nerves and the greater part of the first
thoracic ventral ramus.
 It originates in the neck, passes laterally and inferiorly over rib
I, and enters the axilla.
 The fourth ramus usually gives a branch to the fifth, and the first
thoracic ramus frequently receives a branch from the second.
 Contributions to the plexus by C4 and T2 vary.
 When the branch from C4 is large, that from T2 is frequently
absent and the branch from T1 is reduced, the plexus is called as
prefixed plexus.
 If the branch from C4 is small or absent, the contribution from
C5 is reduced but that from T1 is larger and there is always a
contribution from T2, such type of plexus is called as a postfixed
plexus.

23.  The parts of the brachial plexus, from medial to
lateral, are:-
 The roots
 The trunks
 The divisions
 The cords
 All major nerves that innervate the upper limb
originate from the brachial plexus, mostly from the
cords.
 Proximal parts of the brachial plexus are posterior
to the subclavian artery in the neck, while more
distal regions of the plexus surround the axillary
artery.

24.  Roots
 The roots of the brachial plexus are the anterior rami of C5
to C8, and most of T1.
 The roots and trunks enter the posterior triangle of the neck
by passing between the anterior scalene and middle scalene
muscles and lie superior and posterior to the subclavian
artery.
 Trunks
 The three trunks of the brachial plexus originate from the
roots, pass laterally over the first rib, and enter the axilla.
 The superior trunk is formed by the union of C5 and C6 roots.
 The middle trunk is a continuation of the C7 root.
 The inferior trunk is formed by the union of the C8 and T1 roots.
 The inferior trunk lies on the first rib posterior to the subclavian
artery.
 The middle and superior trunks are more superior in position.

26.  Divisions
 Each of the three trunks of
the brachial plexus divides
into an anterior and a
posterior division.
 The three anterior divisions
form parts of the brachial
plexus that ultimately give
rise to peripheral nerves
associated with the anterior
compartments of the arm
and forearm.
 The three posterior divisions
combine to form parts of the
brachial plexus that give rise
to nerves associated with the
posterior compartments.

27. Cords
 The three cords of the brachial plexus originate from the
divisions and are related to the second part of the axillary
artery.
 The lateral cord
 It is formed by the union of the anterior divisions of the upper
and middle trunks.
 It has contributions from C5 to C7.
 It is positioned lateral to the second part of the axillary
artery.
 The medial cord
 It lies medial to the second part of the axillary artery.
 Is the continuation of the anterior division of the inferior
trunk.
 It contains contributions from C8 and T1.
 The posterior cord
 It lies posterior to the second part of the axillary artery
 It is formed by the union of all three posterior divisions.
 It contains contributions from all roots of the brachial plexus
(C5 to T1).

28.  Roots
 Dorsal scapular nerve (C5)
 Long thoracic nerve (C5, 6, and 7)
 Upper trunk
 Nerve to subclavius (C5 and 6)
 Suprascapular nerve (supplies the
supraspinatus and infraspinatus
muscle.
 Lateral cord
 Lateral pectoral nerve
 Musculocutaneous nerve
 Lateral root of median nerve
 Medial cord
 Medial pectoral nerve
 Medial cutaneous nerve of arm and
medial cutaneous nerve of forearm
 Ulnar nerve
 Medial root of median nerve
 Posterior cord
 Upper and lower subscapular
nerves
 Thoracodorsal nerve
 Axillary nerve
 Radial nerve
Branches of the brachial plexus
The branches of the different parts of the brachial plexus are as
follows:-

30. Branches of the Brachial Plexus Found in
the Axilla.
 The nerve to the subclavius(C5 and 6)
 It supplies the subclavius muscle.
 The long thoracic nerve(C5, 6, and 7)
 It arises from the roots of the brachial plexus in the neck and enters
the axilla by passing down over the lateral border of the 1st rib
behind the axillary vessels and brachial plexus.
 It descends over the lateral surface of the serratus anterior muscle,
which it supplies.
 The lateral pectoral nerve
 It arises from the lateral cord of the brachial plexus and supplies
the pectoralis major muscle.
 The musculocutaneous nerve
 It arises from the lateral cord of the brachial plexus, supplies the
coracobrachialis muscle, and leaves the axilla by piercing that
muscle.

31.  The lateral root of the median nerve
 It is the direct continuation of the lateral cord of the brachial plexus.
 It is joined by the medial root to form the median nerve trunk, and this
passes downward on the lateral side of the axillary artery.

 The median nerve gives off no branches in the axilla.
 The medial pectoral nerve
 It arises from the medial cord of the brachial plexus, supplies and pierces
the pectoralis minor muscle, and supplies the pectoralis major muscle.
 The medial cutaneous nerve of the arm(T1)
 It arises from the medial cord of the brachial plexus and is joined by the
intercostobrachial nerve (lateral cutaneous branch of the 2nd intercostal
nerve).
 It supplies the skin on the medial side of the arm.
 The medial cutaneous nerve of the forearm arises from the medial cord of
the brachial plexus

32.  The ulnar nerve(C8 and T1)
 It arises from the medial cord of the brachial plexus and descends in the
interval between the axillary artery and vein.
 The ulnar nerve gives off no branches in the axilla.
 The medial root of the median nerve
 It arises from the medial cord of the brachial plexus and crosses in front of
the third part of the axillary artery to join the lateral root of the median
nerve.
 The upper and lower subscapular nerves
 It arise from the posterior cord of the brachial plexus and supply the upper
and lower parts of the subscapularis muscle.
 The lower subscapular nerve supplies the teres muscle.
 The thoracodorsal nerve
 Itarises from the posterior cord of the brachial plexus and runs downward
to supply the latissimus dorsi muscle.
 The axillary nerve
 It is one of the terminal branches of the posterior cord of the brachial
plexus. It turns backward and passes through the quadrangular space.
 Then it gives off a branch to the shoulder joint & it divides into anterior
and posterior branches

33.  The radial nerve
 It is the largest branch of the brachial plexus and
lies behind the axillary artery.
 It gives off branches to the long and the medial
heads of the triceps muscle and the posterior
cutaneous nerve of the arm.
 The latter branch is distributed to the skin on the
middle of the back of the arm.

34. Lymph Nodes of the Axilla
 The axillary lymph nodes are 20
to 30 in number.
 They drain lymph vessels from
the lateral quadrants of the
breast, the superficial lymph
vessels from the
thoracoabdominal walls above
the level of the umbilicus, and
the vessels from the upper limb.
 The lymph nodes are arranged in
six groups.
 Anterior (pectoral) group:
 Posterior (subscapular) group:
 Lateral group:
 Central group:
 Infraclavicular (deltopectoral)
group:
 Apical group:

35.  Anterior (pectoral) group:
 Lying along the lower border of the
pectoralis minor behind the pectoralis
major, these nodes receive lymph vessels
from the lateral quadrants of the breast
and superficial vessels from the
anterolateral abdominal wall above the
level of the umbilicus.
 Posterior (subscapular) group:
 Lying in front of the subscapularis
muscle, these nodes receive superficial
lymph vessels from the back, down as far
as the level of the iliac crests.
 Lateral group:
 Lying along the medial side of the
axillary vein, these nodes receive most of
the lymph vessels of the upper limb
(except those superficial vessels draining
the lateral side)

37.  Central group:
 Lying in the center of the axilla in the axillary fat, these nodes
receive lymph from the above three groups.
 Infraclavicular (deltopectoral) group:
 These nodes are not strictly axillary nodes because they are located outside the
axilla.
 They lie in the groove between the deltoid and pectoralis major muscles and
receive superficial lymph vessels from the lateral side of the hand, forearm, and
arm.
 Apical group:
 Lying at the apex of the axilla at the lateral border of the 1st rib, these nodes
receive the efferent lymph vessels from all the other axillary nodes.
 The apical nodes drain into the subclavian lymph trunk.
 On the left side, this trunk drains into the thoracic duct; on the right side, it
drains into the right lymph trunk.
 Alternatively, the lymph trunks may drain directly into one of the large veins at
the root of the neck.

38. Applied Anatomy
 Erbs paralysis
 klumpke’s paralysis
 Injury to nerve toi seratus anterior