pathForResource in subdirectory of directory

I have a bunch of images in a directory called "buttons", which is in a directory called "pictures" and I'm not sure how to access it within my code.I know I can use

Code:

[[NSBundle mainBundle ] pathForResource:ofType:@"png" subdirectory:@"pictures"]

for images in "pictures", but I'm not sure how to access a file in "buttons".