Snail sort

Given an n x n array, return the array elements arranged from outermost elements to the middle element, traveling clockwise.

array = [[1,2,3],  
         [4,5,6],  
         [7,8,9]]

snail(array) #=> [1,2,3,6,9,8,7,4,5]

For better understanding, please follow the numbers of the next array consecutively:

array = [[1,2,3],  
         [8,9,4],  
         [7,6,5]]

snail(array) #=> [1,2,3,4,5,6,7,8,9]  

This image will illustrate things more clearly:

NOTE: The idea is not to sort the elements from the lowest value to the highest; the idea is to traverse the 2-d array in a clockwise snailshell pattern.

NOTE 2: The 0x0 (empty matrix) is represented as en empty array inside an array [[]].