Which of the following planes divides the body into upper and lower parts?

The transverse plane is the correct choice as it divides the body into upper and lower parts. This anatomical plane runs horizontally through the body and is perpendicular to both the sagittal and frontal planes. By slicing the body along this plane, you create a top section (the superior part) and a bottom section (the inferior part), which is fundamental for understanding the orientation of structures within the body.

In contrast, the sagittal plane divides the body into right and left segments and is vital for understanding bilateral symmetry, while the frontal plane, also known as the coronal plane, separates the body into anterior (front) and posterior (back) portions. The dorsal, while generally referring to the back side of the body, is not a plane but rather a directional term and therefore does not serve the purpose of dividing the body into distinct upper and lower sections. Understanding these planes is crucial for massage therapists in both assessing and applying techniques effectively based on the orientation of the body.