The manubrium (or manubrium sterni) is the broad, upper part of the sternum. With a quadrangular shape, wider superiorly and narrower inferiorly, it articulates with the clavicles and the first two ribs.

Features

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Surfaces

Its anterior surface, convex from side to side, concave from above downward, is smooth, and affords attachment on either side to the sternal origins of the pectoralis major and Sternocleidomastoideus. Sometimes the ridges limiting the attachments of these muscles are very distinct. Its posterior surface, concave and smooth, affords attachment on either side to the Sternohyoideus and Sternothyreoideus.

Borders

The superior border is the thickest and presents at its center the jugular or presternal notch; on either side of the notch is an oval articular surface, directed upward, backward, and lateralward, for articulation with the sternal end of the clavicle. The inferior border, oval and rough, is covered in a fresh state with a thin layer of cartilage, for articulation with the body. The lateral borders are each marked above by a depression for the first costal cartilage, and below by a small facet, which, with a similar facet on the upper angle of the body, forms a notch for the reception of the costal cartilage of the second rib. Between the depression for the first costal cartilage and the demi-facet for the second is a narrow, curved edge, which slopes from above downward and medialward.

External links

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Skeletal system