The sternum is a long, flat bone, forming the middle portion of the front of the chest. The top of the sternum supports the clavicles (collarbones) and its edges join with the costal cartilages of the first seven pairs of ribs. The inner surface of the sternum is also the attachment of the sternopericardial ligaments. Its top is also connected to the sternocleidomastoid muscle. The sternum consists of three main parts, listed from the top:
In its natural position,the sternum is angled obliquely, downward and forward. It is slightly convex in front and concave behind; broad above, shaped like a "T", becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. In adults the sternum is on average about 17 cm, longer in the male than in the female.
The manubrium (Latin: handle) is the broad upper part of the sternum. It has a quadrangular shape, narrowing from the top, which gives it four borders. The suprasternal notch (jugular notch) is located in the middle at the upper broadest part of the manubrium. This notch can be felt between the two clavicles. On either side of this notch are the right and left clavicular notches.
The manubrium joins with the body of the sternum, the clavicles and the cartilages of the first pair of ribs. The inferior border, oval and rough, is covered 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 towards the middle. Also, the superior sternopericardial ligament attaches the pericardium to the posterior side of the manubrium.
The body, or gladiolus, is the longest part. It is flat and considered to have only a front and back surface. It is flat on the front, directed upward and forward, and marked by three transverse ridges which cross the bone opposite the third, fourth, and fifth articular depressions. The pectoralis major attaches to it on either side. At the junction of the third and fourth parts of the body is occasionally seen an orifice, the sternal foramen, of varying size and form. The posterior surface, slightly concave, is also marked by three transverse lines, less distinct, however, than those in front; from its lower part, on either side, the transversus thoracis takes origin.