If you're especially concerned about it, a quick phone call to your pediatrician should ease your mind. As many folks have already said here on the board, some kids do traditional crawling, some don't.
But I'm sure it would put your mind at ease to hear that from the professional who has been following your baby's growth and development.
Heh remember, kids do things on their own schedules. The moment you get to the doctor's office will be the moment he decides to crawl
.