Not all drawings are done by starving artists with tortured souls. Before the advent of cameras naturalists had to draw their subjects to record them. Even with cameras some views: sectional cut-aways, internal structure, and extinct species to name a few, are often best illustrated by drawing them.
The site Scientific Illustration has a wonderful collection of these types of drawings. Each has some notes about the drawing, as well as a link to the source of the drawing.
This page has three examples of their collection. There are more examples after the jump.