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Scapula

Other Terms: Shoulder blade

Type

flat

Description

The scapula is a large, flat, triangular bone with three prominent projections. The flattened triangular portion spans from the second to the seventh rib and consists of three borders (superior, lateral, and medial) and three angles (superior, inferior, and lateral). Its lateral angle is conspicuous as it forms the glenoid fossa for articulation with the head of the humerus. Its three prominent projections are the anteriorly facing coracoid process, the posterior ridge termed the spine, and the flat laterally projecting acromion that forms the lateral expansion of the spine. The plate-like body of the scapula is often so thin that it is translucent. (The program includes both true and false views of the scapula. The true views represent those views of the scapula as it would appear when viewed in its articulated position in the body. The false views represent an idealized views of its four surfaces.)

Etymology

Early anatomical texts had varying names for this bone. The early Greeks often called it the omoplate. Hippocrates used the term spathe - meaning a broad, flat instrument - for this bone. The term scapula, also used in early texts, became firmly established in the nomenclature around 1640 and probably derives from the Greek term scapter for a broad flat digging instrument resembling a spade or trowel.

Articulations

The scapula articulates with two bones: the clavicle and the humerus. The acromion articulates via a small articular facet with the acromial end of the clavicle and the glenoid cavity - a smooth, shallow, circular depression - articulates with the head of the humerus.

Ossification

The scapula ossifies from eight separate centers. The first center appears during the eighth embryonic week in the scapular neck. During the third month of intrauterine life additional primary centers form in the acromion, coracoid process, glenoid cavity, inferior angle, and vertebral border. These centers begin to converge. By birth the scapula has its characteristic shape. In addition, two epiphyses form in childhood. One epiphysis arises in the coracoid process, the second epiphysis forms at the junction of the coracoid process and glenoid cavity. These usually fuse with the rest of the scapula sometime between the fourteenth and seventeenth year.

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