When comic book superheroes ushered in a modern sort of mythology, it was only fitting that one them resembled a figure from ancient mythology. As comics' first super-speedster, the most distinctive feature of the Flash's costume was the winged, wide-brimmed helmet that evoked Hermes, the fleet-footed messenger of the Greek gods, later renamed "Mercury" when the Romans co-opted the Greek deities.
However, there was one feature of Jay Garrick's original costume that definitely wasn't based on ancient images of Hermes. Appearing on the cover of Flash Comics #1 (1940), check out the snazzy yellow lightning bolts adorning Jay's blue pants!
(click on the image for a larger view)
The "leg lighting" only stuck around for two issues...or, to be more precise, one and a half issues. By the middle of Flash Comics #2, the leg lightning started popping in and out, until finally disappearing for good by the story's end.
From that point forward, the leg lightning was history...with only a few random exceptions over the next year or so. Sometimes a tiny icon of a lightning-legged Flash would appear on covers that featured other characters from the anthology title (such as Hawkman), yet the interior stories stuck with the lightning-free blue pants (click on the icon art to the left for a closer look).
When the cover icon was discontinued after issue #7, the last remnant of the leg lightning had faded away. That is, until it inexplicably returned on the covers of Flash Comics #8 and #10... as well as in an utterly random single panel in issue #13! (click to enlarge)
Were there any additional appearances of Flash's infamous lightning legs? I'm not sure...but maybe my pals over at the Flash-centric Speed Force website have more to add.