Vent blocks?

[Ravendance]

We're building our first little house, 12x16 with a sloped (not gable) roof, using the Little House Plans Kit. I'm confused about the placement of "vent blocks" (plan page 5/9), which are described as "2x4x16 centered @ each rafter." Can anybody offer this newbie a bit more clarification? I can't visualize the placement in relation to the intersection of the walls (top plate), and the rafters. (we're not using ceiling joists.)
What am I missing here?

[Jeff922]

Here's some pics of mine.  There are many ways to do it.  If I were to do this again, I'd have them hang over the top-plate 3/4" so the sheathing could butt up under it.  Also use a heavy, metal screening so critters can't get through it.