I'd be ok with any of these: head/last head/tail front/back current/last curr/last car_bonnet/car_boot (just kidding ;))
But beyond that, I'd sooner choose "head/foot" over "head/toe". If array-style indexing were ever done, I'd be against using negative values to indicate distance from end. The semantics of a paramater should never be dependant on the paramater's value. (I think that classic book "Writing Solid Code" called that a "candy-machine interface", IIRC? Or maybe that as something different.)
