Inferior to the xyphoid process, readymade internal heart spike.
oh boy, the xiphoid process. Now there's a flawed piece of engineering if i ever saw one.
So for you laypersons out there, you've got a chest bone that your ribs attach to. This is your sternum. It provides structure and support for the rib cage, along with the shape of the chest itself. (Overgrowth of the sternum is usually the root cause of pectus carinatum, where the chest juts outwards in an almost tentlike, sorta-triangular shape.)
At the top of the sternum is the manubrium. The manubrium joins with the clavicles (collarbones), the cartilage of the first ribs, and some muscles. I believe there's also a ligament attached to the manubrium that is itself connected to the pericardium, the sac around the heart. The manubrium is thick, and very strong.
The body of the sternum, sometimes itself called the sternum, sometimes also called the gladiolus. The body of the sternum connects to the second through sixth ribs, the manubrium at the top, and the xiphoid process at the bottom. The major chest muscle
pectoralis major attaches to the body of the sternum. It is quite easy to feel for the manubriosternal joint, where the manubrium and the body of the sternum join. Follow your collarbones towards your chest until you feel a bone between the end of the collarbones, below where the soft part of your neck ends. This is the manubrium. Follow the manubrium down a few cm until you feel a jutting bone. In some people, this is hard to detect, in others, it is extremely prominent.
This is where the manubrium and the body of the sternum meet.
Both the body of the sternum and the manubrium are quite strong and provide structure. It takes a large amount of force to break the sternum, by which time the ribs are probably already broken themselves.
Lastly, the odd one out: The Xiphoid process. It's a triangular, rather pointy process (outcropping of bone) that attaches to the base of the sternum with rather less interface in the fibrous joint than the manubriosternal joint has. It is for this reason that you must be careful when doing CPR, as if your pressure lies too low on the sternum, you can quite easily snap the xiphoid process off entirely, often puncturing either the diaphragm or the liver. In the case of the liver, this can be lethal.
The only true function of the xiphoid process is for costal cartilage (cartilage that extends the ribs outwards) to attach to and reinforce. Additionally, the cartilage within the solar or celiac plexus, a bundle of nerves enervating the stomach and diaphragm, reside here. It is for this reason that a blow to the stomach or slightly higher can cause initial difficulty breathing "having the wind knocked out of you".
For what it's worth, the xiphoid process is more of a liability than a help to humanity. In other animals, it is much the same, but as bipeds it is more exposed for us. The only animal to have a major, well developed xiphoid would be flying birds, which follows their keel bone, which is an extended sternum.
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Topic: Things that made you go "WTF?" today o_O (Read 14848838 times)