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.
The sternum, also known as the breastbone, is the bone located in the center of the chest where the upper ribs converge.