Get directory name?

[Lennart Borgman (gmail)]

I can't find a good way to get the last directory name from a directory
path using the current functions for file name handling. There must be
some way ...?

file-name-nondirectory does not work for a directory path (or, rather it
returns "" which is not what I want). Maybe there should be a

(defun  directory-last-name (directory)
  "Returns the last name in a directory path.
..."