The Pectoral Region

Question 1

What are the lines of orientation in the pectoral region.

Answer 1

1. Midsternal line: It runs vertically downwards in the
   median plane on the front of the sternum.
2. Midclavicular line: It runs vertically downwards from
   the midpoint of the clavicle to the midinguinal point.
3. Anterior axillary line: It runs vertically downwards from
   the anterior axillary fold.
4. Midaxillary line: It runs vertically downwards from a
   point located midway between the anterior and posterior
   axillary folds.
5. Posterior axillary line: It runs vertically downwards
   from the posterior axillary fold.

Question 2

Identify the cutaneous innervation of the pectoral region.

Answer 2

1. The skin above the horizontal line drawn at the level of
   sternal angle is supplied by supraclavicular nerves (C3
   and C4).
2. The skin below this horizontal line is supplied by
   anterior and lateral cutaneous branches of the 2nd–6th
   intercostal nerves (T2–T6).

Question 3

Name 4 muscles in the pectoral region.

Answer 3

1. Pectoralis major.
2. Pectoralis minor.
3. Subclavius.
4. Serratus anterior.*

Question 4

Which is the largest muscle in the pectoral region.

Answer 4

Pectoralis major

Question 5

Identify the origin, insertion, nerve supply, blood supply and actions of pectoralis major muscle.

Answer 5

Origin: Clavicular head—arises from the medial half of the anterior aspect of the clavicle.
Sternocostal head—arises from the (a) lateral half of the anterior surface of the sternum (b) first seven costal cartilages, (c) aponeurosis of the external oblique muscle of the abdomen.
Insertion: Lateral lip of intertubercular
sulcus of humerus (bicipital groove)
Nerve supply: Nerve supply is by lateral (C5 to C7) and medial pectoral (C8 and T1) nerves.
Action: The clavicular head flexes the arm, whereas sternocostal head
adducts and medially rotates the arm.

Question 6

Identify the origin, insertion, nerve supply, blood supply and actions of the pectoralis minor muscle.

Answer 6

Origin: It arises from 3rd, 4th, and 5th ribs, near their costal
cartilages.
Insertion: Coracoid process of scapula.
Nerve supply: medial pectoral nerves
Action: Depresses tip of shoulder, protracts scapula, acts as an accessory muscle of respiration during forced inspiration.

Question 7

Identify the origin, insertion, nerve supply, blood supply and actions of the subclavius muscle.

Answer 7

Origin: First rib at the costochondral cartilage.
Insertion: Subclavian groove of the clavicle.
Nerve supply: Nerve to subclavius.
Actions: Pulls clavicle medially to stabilize sternoclavicular joint,
depresses tip of shoulder

Question 8

Identify the origin, Insertion, nerve supply, blood supply and actions of the serratus anterior muscle.

Answer 8

NB: Not a muscle of the pectoral region.
Origin: It arises by a series of 8 digitations from upper eight ribs. The
first digitation arises from the 1st and 2nd ribs, whereas all
other digitations arise from their corresponding ribs.
Insertion: It is inserted into the costal surface of the scapula along its
medial border. (The first 2 digitations are inserted into the
superior angle, next 2 digitations into the medial border and
the lower 4 digitations into the inferior angle of the scapula.)
Nerve Supply: It is by long thoracic nerve/nerve to serratus anterior(C5, C6, and C7).
Actions: 1. It is a powerful protractor of the scapula, i.e., it pulls the
scapula forward around the chest wall for pushing and
punching movements as required during boxing. Hence,
serratus anterior is also called boxer’s muscle.
2. It keeps the medial/vertebral border of scapula in firm
contact with the chest wall.
3. Its lower 4 or 5 digitations along with lower part of the
trapezius rotate the scapula laterally and upwards during
overhead abduction of the arm.

Question 9

Identify the location and extent of the pectoral fascia.

Answer 9

Location: It is the deep fascia covering the anterior aspect of the
pectoralis major muscle.
Extent:
1. Superiorly, it is attached to the clavicle.
2. Inferiorly, it is continuous with the fascia of anterior
abdominal wall.
3. Superolaterally, it passes over the deltopectoral groove
to become continuous with the fascia covering the
deltoid muscle.
4. Inferolaterally, it curves round the inferolateral border
of the pectoralis major to become continuous with the
axillary fascia.

Question 10

Identify the location of the clavipectoral fascia.

Answer 10

The clavipectoral fascia is a strong fascial sheet deep to the
clavicular head of the pectoralis major muscle, filling the
space between the clavicle and the pectoralis minor muscle.

Question 11

What are the structures that pierce through the clavipectoral fascia?

Answer 11

Structures Piercing the Clavipectoral Fascia:
1. Lateral pectoral nerve.
2. Thoraco-acromial artery.
3. Lymphatics from the breast to the apical group of
axillary group of lymph nodes.
4. Cephalic vein.

Question 12

Name the muscles enclosed by the clavipectoral fascia.

Answer 12

subclavius and pectoralis minor.

Question 13

Name two muscles of the upper limb supplied by all 5 spinal segments of the brachial plexus.

Answer 13

The pectoralis major and pectoralis minor muscles.

Question 14

Which muscle of the axilla/pectoral region is considered key and why?

Answer 14

Pectoralis minor - because it crosses the axillary artery and divides it into 3 parts.