In the second picture, you see that part you've circled? That part of the strap is the same to the part you've circled in the first picture. The first picture is the complete rear cinch while the second picture has the rear cinch down to where those buckles are on the first picture.
The difference between the two is that the second picture/second rear cinch is a bit fancier in how it attaches to the saddle. The first one ties on to the saddle, like the top of a latigo does, while the second kinda wraps itself on.
Hopefully that makes sense?
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.