The Scapula is a flat, triangular bone having two surfaces, anterior and posterior, and three margins, vertebral, axillary, and superior. Between the upper and second fourth of the vertebral border on the posterior surface there starts a process, which passes right across the dorsum of the bone, and ends in the acromion process. From the external end of the superior border projects a beak-like process called the coracoid. Immediately to the inner side of the root of the coracoid process is the suprascapular notch.

Fig. 2. The Right Scapula (Posterior View).

The superior angle (vertebral end of superior border) is more or less rectangular, and the inferior angle very acute. At the junction of the outer end of the superior border and the upper end of the axillary border is the glenoid cavity, a pyriform, slightly concave area, which receives the head of the humerus, thus forming the shoulder-joint. The coracoid process arises just internal to the glenoid cavity, and, bending on itself forwards and outwards, overhangs the glenoid surface; it is very much roughened for the attachment of muscles and ligaments.

The anterior, or ventral, surface of the bone is concave, and has several rough lines on it, caused by the attachment of the subscapular muscle. The axillary border on this surface is full and rounded, the vertebral border being roughened. Both borders give attachment to muscles.

The posterior dorsal surface is divided into an upper smaller fossa and a lower larger fossa by the spine, which runs from the vertebral border outwards and upwards to the glenoid cavity. Both fossae give attachment to muscles. The spine is separated from the edge of the glenoid cavity by the great scapular notch; the posterior border is subcutaneous, and is lipped for the attachment of muscles; at the great scapular notch it is flattened to form the acromion process, which passes forwards and outwards to overhang the joint, and gives attachment to muscles and ligaments.

The scapula articulates by means of the glenoid cavity with the head of the humerus, and by the acromion process with the acromial end of the clavicle.

Ossification

At birth the coracoid and acromion processes, the glenoid cavity, and vertebral border are still cartilaginous. Secondary centres appear in these from birth up to puberty, and the bone is complete about the twentieth year.