You can ask for the corner values one at a time just by indexing into the array. And just like regular python lists, you can use the -1 index for the last value. So the corner values are [0,0], [0,-1], [-1,0], and [-1,-1], for any 2D array.
>>> niner = np.array(range(81)).reshape(9,9)
>>> print(niner[-1,0])
72
Or to combine them into a new array with advanced indexing, we can give all the rows we want and all the columns we want:
>>> print(niner[[0,0,-1,-1],[0,-1,0,-1]])
[ 0 8 72 80]