This issue has come up in Question 21.1 from the first paper of 2014. The candidates were invited to label a diagram of a dermatome-mapped homunculus. In order to supply the candidates with a readily available visual reference for this question, I have reproduced two free Wikipedia images in this revision article.
For a more detailed look, one can see the textbook "Neurosurgical Classics".
Foerster, O. "The dermatomes in man." Neurosurgical Classics (1992): 129. Best viewed in this Googlebook.
Additionally, here is a link to the Wikipedia page I robbed.