Here's what a single book looks like in the traditional publishing model. (Click or open in a new window to enlarge.) Obviously this flow isn't completely accurate, because for instance some readers will get to the book before reviewers and the publisher's marketing staff may still be doing work after the book is produced, etc.
Note the money flows from the readers to the booksellers to the publisher. The publisher pays the bookbinders, editors, cover artist, marketing personnel, agent, and author. The agent obviously pays their own staff, and you'll note that in this model no money flows from the author (unless he has a personal staff.) Remember that any agent or publisher who asks an author for money is a scam artist.
It's also interesting to note just how many people involved in this process don't get paid period. Libraries are obviously supported by the public and don't get money from book sales. Reviewers for the most part don't get paid (although if they do it would be by the publisher or author.) Professional organizations are supported by dues-paying members. For the most part, beta readers, critique groups, and other authors are involved in the process out of love.
And just to be clear, here's what this would look like in the self-publishing world. The main difference, you'll note, is that the publisher and the agent are cut out. Pay goes directly from the bookseller to the author, who then pays for marketing, editing, cover design, etc. I pondered representing the real danger of self publishing by cutting back seriously on the number of readers. But the truth is, a self-published author has the potential to reach as many readers as a traditionally published author, so in a sense the pool is the same. Many self-published authors make more than they would have through traditional publishing, because of how this process is streamlined. But this is more the exception than the norm.
Green crayon - money flow
Black - producing the manuscript
Tan - representing the manuscript
Red - publishing the manuscript
Blue - producing and distributing the book
Orange - promoting the book
Purple - terminal