You'll need to get a usb-serial adapter and then connect with a console cable.
Connecting to the Console Port with Mac OS X. To connect a Mac OS X system USB port to the console using the built-in OS X Terminal utility, follow these steps:
Step 1. Use the Finder to go to Applications > Utilities > Terminal.
Step 2. Connect the OS X USB port to the router.
Step 3. Enter the following commands to find the OS X USB port number: