Xiphoid process
The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...

 (extension) of the lower part of the sternum which is usually ossified
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...

 in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major joints, this is non-movable. Much the way the first seven ribs articulate with the sternum, the cartilage in the celiac plexus
Celiac plexus
The celiac plexus or coeliac plexus, also known as the solar plexus, is a complex network of nerves located in the abdomen, where the celiac trunk, superior mesenteric artery, and renal arteries branch from the abdominal aorta...

 joins on the xiphoid process, reinforcing it, and indirectly attaches the costal cartilage to the sternum.