Here is a good link that shows great pictures of great and poor examples of the breed. It has good pictures of dogs with good bone and what bad bone looks like. Great good and bad examples of head shots etc. Copy and paste this to your search engine.
http://www.everythingneo.com/standard.html

Neapolitan Mastiffs are now so famous that they even reach Hollywood. They have invaded Hogwarts and one is a pet of our good friend Hagrid. :)