Final answer:
The mid-sagittal plane divides the thorax into equal anterior and posterior parts.
Step-by-step explanation:
The plane of the body that divides the thorax into equal anterior and posterior parts is called the mid-sagittal plane. This plane runs vertically through the midline of the body, separating it into right and left halves. It is also known as the median plane.
For example, if you were to cut a human body directly down the middle, from top to bottom, you would be dividing it into equal anterior (front) and posterior (back) portions.