Model T gas tank?

[marty in Ohio]

I'm an "A" guy but yesterday at a car show I met a "T" guy who was showing a 1926 or '27. Being unfamiliar with the "T" I looked it over pretty good. I noticed that the coil boxes were under the hood and started looking further. I saw that the gas tank was in the cowl on the right side behind the dash board. I asked the owner how the tank was filled and he opened, what I thought, was a vent on top of the cowl and there was a gas cap. Was this original or was this a modification? I thought all Model T's had their tanks under the seat. Somebody please set me straight.
Marty in Ohio