Pectoral Girdle

The pectoral girdle refers to the shoulder region which attaches the upper arm to the axial skeleton. Thus, the pectoral girdle and upper limb are closely associated with each other. This girdle, which is also called the shoulder girdle, consists of two bones that make up the shoulder. This is an important girdle in the body as it has the responsibility of providing basic structural support along with an area for attachment to the various muscles that are present in this region. As there is no posterior attachment, the shoulder girdle has a high range of motion. Given below are details regarding the bones and muscles associated with the shoulder girdle.

Bones of Pectoral Girdle

Scapula: The scapula is also known as the shoulder blade. This is the bone which connects the humerus (bone of the upper arm) with the clavicle. The scapula forms the posterior part of the shoulder girdle in humans. This is a flat bone which is roughly triangular in shape. It is placed on the posterolateral aspect of the thoracic cage. The ventral surface presents a broad concavity which is known as the subscapular fossa. The scapula is an important bone as it provides attachment to various muscles of the head, neck and back region.

Clavicle: The clavicle, also known as the collarbone is a small 'S' shaped bone which makes up the shoulder girdle along with the scapula. It is a doubly curved short bone that connects arm to the body and is located directly above the first rib. The clavicle aids in pectoral girdle function of keeping the arm away from the thorax and the central skeleton thereby ensuring that the arm is allowed to perform a large range of motion with relative ease. It also acts as a rigid support from where the scapula and upper limb are suspended.

Pectoral Girdle Muscles

Pectoralis Major: This is one of the main muscles involved with the pectoral girdle. This is a fan-shaped muscle that covers the superior part of the thorax. Its origin lies in the clavicular head and the sternocostal head. When both these parts of the muscle act together, then the pectoralis major adducts and medially rotates the humerus at the shoulder joint. This muscle is innervated by the lateral and medial pectoral nerves.

Pectoralis Minor: The pectoralis minor is also one of the pectoral muscles which is present in the anterior wall of the axilla. This muscle is largely covered by the pectoralis major. It is innervated by the medial pectoral nerve. It is attached to the ribs near the costal cartilages and is also attached to the coracoid process of the scapula.

Serratus Anterior: The serratus anterior is a large muscle that lies in the lateral part of the thorax. It is proximally attached to all the ribs and is distally attached to the medial border of the scapula. It is innervated by the long thoracic nerve. This is the muscle that is responsible for protraction of the scapula and it holds and fixes it against the thoracic wall. It is activated when punching a person and hence, is also known as 'the boxer's muscle'.

There are also a few more muscles that are involved with the pectoral girdle in an indirect manner, that is, they are attached to the scapula or the clavicle but only partly help in its movement. These include subclavius, levator scapulae, rhomboideus and trapezius muscle. This was all about this important girdle which aids in connecting the upper limb to the axial skeleton.