What is a Pectoral Girdle? 

A pair of structures that connect the axial skeleton to the upper limbs is known as the pectoral girdle. It forms articulations, or joints, with the upper limbs, each consisting of a clavicle and scapula.  

Structure of the Pectoral Girdle 

The human body's left and right pectoral girdles each contain two bones, the scapula and clavicle. The scapulae articulate medially (toward the midline of the body) with the vertebral column and laterally (away from the body's midline) with the clavicle and the upper arm's humerus bone. The clavicles attach to the sternum (breastbone) and the scapulae medially and laterally. The actions performed by the upper limbs cannot be done without the assistance of the pectoral girdle, whether the action is elevating the shoulders or carrying the arm to the body. 

The Function of the Pectoral Girdle 

The pectoral girdle does more than linking the upper limbs and the axial skeleton. It holds the shoulders in place and serves as a foundation for arm movement. It is a point of connection for several muscles in the back, chest, and neck that aid in the movement of the upper limbs. The pectoral girdle is unusual in that it can pass in a variety of directions. This property of the pectoral girdle is due to the scapula's loose attachment to the axial skeleton, which causes it to shift back and forth towards the thorax (rib cage) with muscular movement. There is no articulation stage between the pectoral girdles and the vertebral column, which allows for a full range of motion in the arm. Thus, people may move their arms away, toward, or even above their heads. The relation between the humerus and the scapula is another anatomical function of the pectoral girdle that contributes to mobility. Since this bone connection is shallow, it allows for a wide range of upper limb movement. 

Anatomy of the Scapula 

The scapula, or shoulder blade, is a triangular flat bone in the pectoral girdle's posterior portion. The scapula's main purpose is to attach the humerus (upper arm bone) to the clavicle (collarbone). On the upper back near the elbow, the scapula may be palpated or felt at the surface of the skin. The scapula's loose attachment to the axial skeleton (specifically the rib cage) allows it to move freely across the thorax. Movements may happen on their own or in response to arm movements. 

Because of its triangular shape, the scapula has three main regions: three sides and three angles. Superior, medial, and lateral are the names of the sides, and superior, lateral, and inferior are the names of the angles. The superior border of the scapula is a small, sharp, and short horizontal edge that runs along the top of the scapula. At the superior angle of the scapula, it connects with the medial margin. The medial (or vertebral) boundary is the edge that runs parallel to the vertebral column and is close to the vertebrae. 

A thick border near the axillary (underarm) area is known as the lateral (or axillary) border. At the lateral angle, the lateral boundary attaches to the superior border, and at the inferior angle, it connects to the medial border. 

The acromion, a broad protrusion from the posterior (back) side, and the coracoid process, a finger-like projection from the anterior (front) side, make up the lateral angle. At the acromioclavicular joint, the scapula's acromion area articulates with the clavicle. The glenoid cavity, a shallow cavity shaped in the scapula where the humerus articulates with the pectoral girdle, is located inside the lateral angle. When the glenoid cavity's scapula articulates with the upper limb's humerus, the glenohumeral joint, or shoulder joint, is shaped. The shoulder joint looks like a socket or cup-like opening into which the humerus head fits. The glenoid cavity's edges act as attachment points for the shoulder and arm muscles. A prominent ridge extends almost horizontally from the acromion to the medial boundary on the posterior side of the scapula. 

Anatomy of the Clavicle 

The clavicle, which is part of the pectoral girdle, works with the scapula to support upper limb stabilization and movement. 

The clavicle, also known as the collarbone, is a long, S-shaped bone that runs horizontally between the scapula and the sternum (breastbone). It is made up of two parts: a round end and a flattened end. The medial or sternal end, which is the portion of the clavicle that articulates with the top region of the sternum, has a rounded end (manubrium). The sternoclavicular joint is the name for this articulation. The long, flat side of the clavicle that articulates with the acromial process of the scapula to form a shoulder joint is known as the lateral or acromial end. The superior (upper) surface of the clavicle is smooth, while the inferior (lower) surface has grooves and ridges. These bone marks act as muscle and ligament attachment points. 

At the base of the spine, the whole length of the clavicle may be palpated or felt. It connects the upper arms to the body and holds the shoulders in place by acting as a support for the scapula. As a result, the shoulder joint is positioned to allow the upper limb to move in a wide range of motion. The shoulder folds inward and backward when the clavicle is broken. One of the most frequently broken bones in the body is the clavicle.  

Clavicle fragility varies with age. Since the paired bones are brittle and more likely to break in babies, their clavicles are extremely fragile. The same is true for young children, whose bones are still small. Adults are less likely to break their clavicle because it thickens with age. 

Anatomy of the Arm and Forearm 

Three long bones make up the arm and forearm. The humerus, situated between the shoulder and the elbow, is the largest bone in the upper limb. It is the only bone in the upper arm area. At the elbow, the humerus articulates with the scapula proximally (closer to the body's center). The humerus articulates with the bones of the forearm to form the elbow joint at its distal end (further away from the center of the body). 

Context and Applications   

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors of Science in Zoology 
• Bachelors of Science in General Physiology 
• Master of Science in Human Physiology   
• Master of Science in Anatomy and Physiology 

Related Concepts 

1. The skeletal system of human 
2. Skeletal muscles 

Practice Problems 

1. What is the acromioclavicular joint? 

The acromioclavicular joint is also referred to as the AC joint because they are formed by joining the acromion process of the scapula and clavicle bone. This joint is known to comprise the shoulder complex. The AC joint is torn in weight-lifters, and its breakdown generally causes arthritis fractures and separations. 

2. What is a sternoclavicular joint? 

The sternoclavicular joint, commonly referred to as SCJ, is the articulation formed between the sternum and the clavicle bone. This joint helps in the increased rate of mobility by accommodating the movements of the upper limbs. It also aids in connecting the upper limbs to the axial skeleton.