There are two muscles found in the thoratic wall of the cat that  are not found in humans. Those two are, the xiphihumeralis and the  pectiantebrachiales.
Sternum - Structure. 1  The sternum is a long, flat bone, forming the middle portion of the front of the chest. 2  Manubrium. 3  Xiphoid process. 4  In its natural position, the sternum is angled obliquely, downward and forward. 5  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.
Sternum pain is a sharp, usually unexpected pain in the chest area. The pain is sometimes associated with myocardial infarction (MI) or heart attack because of the similar sharp pain felt by the sufferer. Sternum pain is characterized by a radiating paineither in the inferior side or sides of the breast bone. In certain cases, the pain is accompanied with tenderness and swelling accompanied by a cracking sound from the sternum joints. Such a condition is referred to as popping sternum.