How to view the original mail information from gmail? (mail header)

Gmail is a Web mail. We use  "View Source" on the page, that is page's code only. If you want to see the original letter of information, they can actually from the top-right corner of the letter Reply button and drop-down arrow beside it right to expand more options. Choise "Show original "(will open another web page) to see the original information about this mail.

 Dorp-down arrow beside right  "Replay" than choise「Show original」.