Hello Stretched Bird Base question

Hello all:

  New folder here but quite good at following direction and using diagrams!
I am having great problems with the "stretched bird base". It seems no
matter what book or what diagram I look at/search for, there are no diagrams
of the inside of the stretched bird base!
One diagram says "stretch for a different internal structure" what the heck
is that supposed to mean? another says "fold side down". down? down where?
Sideways, longways? I am working on the hummingbird model and cannot go
further without some explanation of what the stretched bird base looks like
inside!

coffy
-- 
For Duty and Humanity!