Snail

snail = function(arr) {
  var top, bottom, left, right;

  if (arr.length === 0) return [];
  if (arr.length === 1) return arr[0];

  top    = arr.shift();
  bottom = arr.pop().reverse();
  right  = [];
  left   = [];

  arr.forEach(function (elem) {
    right.push(elem.pop());
    left.unshift(elem.shift());
  });

  return [].concat(top, right, bottom, left, snail(arr));
}