I want to do an MEG analysis and first I want to downsample the surface to around 100 vertices per hemisphere.  I tried the command mris_downsample, but when i plot the surface I see that the vertices go deep into the white matter. 

Is there an option to extract for example 100 equidistant vertices from a fsaverage?  Maybe knowing  how the vertices are organized when saved would help, so for example, when I load a surface in matlab the vertices are shown as a vector, is there a way to know the spatial order?

Thanks

Dorothy