How to access cygwin commands without having to include path?

How do I access Cygwin commands from Matlab without having to include the path? I am using the evaluation version of R2016b on Windows 10. I just installed Cygwin, and added all Cygwin paths to my matlab directory as,

   path(path, genpath('C:\cygwin64\'));

However I can't get the ls command to run with the ! escape ,

    !ls
'ls' is not recognized as an internal or external command, 
operable program or batch file.

It works if the full path is specified,

    !C:\cygwin64\bin\ls

But I don't want to have to type the path. How can I make Matlab run Cygwin commands without having to type the path?