The very back of the system has a cartridge slot, a power plug hole and a shoulder button on either side. (digitaltrends.com)
There are also some additional control options that make use of the PlayStation Vita's functions, such as peeking around corners using the touchscreen or item selection using the touch pad on the back of the system. (metalgearinformer.com)
He mentioned you can now slit enemy throats by wiping over the trackpad on the back of the system. (metalgearinformer.com)