The correct answer is C. Septum.
The septum is a muscular wall that separates the right and left sides of the heart. It is made up of two parts: the interventricular septum and the interatrial septum. The interventricular septum separates the right and left ventricles, while the interatrial septum separates the right and left atria.
The septum is important because it prevents blood from mixing between the right and left sides of the heart. This is necessary because the right side of the heart pumps blood to the lungs, while the left side of the heart pumps blood to the rest of the body. If blood were to mix between the two sides of the heart, it would not be able to deliver oxygen-rich blood to the rest of the body.
A. Keratin is a protein that is found in the hair, skin, and nails. It is not a muscle.
B. Maxilla is the upper jaw. It is not a muscle.
D. Tubercles are small, round bumps that can form on the skin. They are not muscles.