Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Ribbon diagram, first viewed perpendicular to the tunnel axis, then viewed along the tunnel axis, then rotated back to initial view with two apposing chains displayed.
