To measure the area of Anne's upper lung (image 4/9), you'll first need to trace an outline of the tissue. Be sure Polygon and Area are selected in the pull-down menus next to the Draw and Measure buttons.

Click Draw, and use the mouse to trace the outline of one lung; a small square will appear at your starting point. Continue tracing around the lung, clicking every time you want to change direction. Then cross over to the second lung so that your polygon forms a figure 8 pattern, as shown: Do not include the trachea. When you finish the outline, you should be back at the initial square. Click the square to close your polygon.

Click Measure to see the area in the Measure Results box. You'll need this polygon again, so DO NOT click outside the image (unless you don't mind re-tracing it).