The term Dividing Membrane is composed of two words, DIAPHRAGM and SEPTUM. A DIAPHRAGM is a thin sheet of muscle that separates the thoracic cavity from the abdominal cavity in mammals. It is also used to control breathing. A septum is a wall or membrane that divides two cavities or spaces. In the human body, it can be found in the nose, separating the nostrils, and in the heart, separating the left and right atria. Together, these two terms refer to a dividing membrane that separates two cavities or spaces.