(hopefully) simple array op

I have a multidimensional array "a", for example,

a

, , 1

    [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 2

    [,1] [,2]
[1,]    5    7
[2,]    6    8

So a is 2x2x2.

I have another array "b", for example,

b

    [,1] [,2]
[1,]    9   11
[2,]   10   12

So b is 2x2.

I want to "tack" b onto a so that b becomes a new "plane", so to  
speak,
in a.  In other words, I want the result c to be:

c

, , 1

    [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 2

    [,1] [,2]
[1,]    5    7
[2,]    6    8

, , 3

    [,1] [,2]
[1,]    9   11
[2,]   10   12

I can think of a number of ways to do this, but they are all  
cumbersome.
Given R's facility with arrays and indices, it occurs to me that there
might be some "one-line" way to accomplish this.  Does anyone know if
there is?  Thanks.

--Sam