Fischer Projections confusion
The carbon chain of a fischer projection is drawn vertically. 

Yes, the vertical and horizontal lines depict 'into the page' and 'out of the page' respectively. 

However, when you have a carbon chain with more than 3 carbons, each down carbon on the backbone which would normally be projected away from you (according to the above rule) has to be rotated. Essentially, this creates the 'zig-zag' you would see in other projections (e.g. Natta Projection).