The xiphoid process is the smallest of the three pieces: it is thin and elongated, cartilaginous in structure in youth, but more or less ossified at its upper part in the adult.
Surfaces.—Its anterior surface affords attachment on either side to the anterior costoxiphoid ligament and a small part of the Rectus abdominis; its posterior surface, to the posterior costoxiphoid ligament and to some of the fibers of the diaphragm and Transversus thoracis, its lateral borders, to the aponeuroses of the abdominal muscles. Above, it articulates with the lower end of the body, and on the front of each superior angle presents a facet for part of the cartilage of the seventh rib; below, by its pointed extremity, it gives attachment to the linea alba. The xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one or other side.
Structure.—The sternum is composed of highly vascular cancellous tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles.