The pectoral girdle is a part of the appendicular skeleton, which connects the upper limbs to the axial skeleton. The human skeleton is divided into two sections, the axial skeleton and the appendicular skeleton.
Axial skeleton is made up of 80 bones and includes the skull, the vertebral column, ribs and the sternum.
Appendicular skeleton is made up of 126 bones and includes the pectoral girdle, the pelvic girdle and limbs.
The pectoral girdle is also known as shoulder girdle. It constitutes the shoulder part and also the attachment site for the humerus.
Pectoral Girdle Bones
Pectoral girdle can be divided into two equal halves. Each half of the pectoral girdle consists of two bones, namely scapula (shoulder blade) and clavicle (collar bone). It helps in the articulation of upper limbs to the axial skeleton. It aids in the movement of arms and shoulders. The right and left parts are not joined together and it allows independent movement.
The main parts of the pectoral girdle are:
Scapula (Shoulder blade)
It is a triangular-shaped flat bone, which forms the posterior side of the shoulder. It is present dorsally in the thorax region between the second and the seventh ribs.
- Spine of scapula- It is an elevated ridge present on the posterior side of the scapula. It divides the convex posterior portion of the scapula into the smaller supraspinous fossa and the bigger infraspinous fossa.
- The ventral surface of the scapula faces ribs and there is a concave depression, which is known as subscapular fossa.
- Acromion- It is a flat and expanded process. The spine extends laterally to form acromion. It articulates with the clavicle by acromioclavicular joint. It forms an arch over the glenohumeral joint.
- Glenoid cavity- It is present below the acromion. It is in the form of depression at the lateral surface of the scapula. The head of the humerus articulates at the glenoid cavity by glenohumeral joint.
- Coracoid process- It is a hook-like projection present above the glenoid cavity and below the clavicle. It is attached to the clavicle by a ligament. Muscles of arms and chest attach here.
Clavicle (Collar bone)
It is a long s-shaped bone, which forms the anterior part of the pectoral girdle. It is present horizontally and is also known as the collar bone.
- The main function of the clavicle is that it attaches the upper limb to the sternum (axial skeleton) and transmits forces from the upper limb to the axial skeleton. It also protects the underlying nerves and vasculature, which connects the upper limb to the trunk.
- On one side, it articulates with the sternum and on the other side, it articulates with the acromion.
- The large and triangular sternal end is also known as the medial part, which articulates with the manubrium of the sternum by sternoclavicular joint. It is supported by the costoclavicular ligament or rhomboid ligament present between the clavicle and the first rib.
- The shaft portion is the attachment site of many muscles, e.g. deltoid. trapezius, sternohyoid, etc.
- The acromial end is also known as the lateral part. It articulates with the acromion of the scapula by acromioclavicular joint. It forms the bony tip of the shoulder laterally. Conoid and trapezoid ligaments are also attached to it.
Also see: Locomotion and Movement
To sum up, the pectoral girdle is made up of two bones, scapula and clavicle. It connects the upper limb to the trunk. The Pectoral girdle is only connected by ligaments to the vertebral column so there is more range of movement compared to the pelvic girdle. The sternoclavicular joints on both sides are the only true joints between the pectoral girdle and the axial skeleton.
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