This is the precise opposite of what you see in Diplodocus according to Stevens et al. where vertical flexibility is considerable but there is relatively little horizontal flexibility. It fits a little better what you see in Apatosaurus, but Apatosaurus has a proportionately shorter neck than Diplodocus. This suggests that whatever the purpose of the really freakin' long neck seen in some sauropods was, at least in the diplodocids it wasn't to forage on the ground.