I find old patent applications to be extremely interesting from a historic, aesthetic and engineering perspective. Above is the engineering drawing that accompanied the 1875 patent for the tricycle.
The inventor, George W. Marble, did not call it a tricycle but rather a velocipede, a late 19th century, general description for any self-propelled vehicle. He also didn't think it was for girls. Here is how he put it in his application: "The nature of my invention relates to an improvement in velocipedes of the tricycle variety, and has for its object to construct a light, strong, and durable vehicle for boys use, and to simplify and reduce the cost of construction."
It's interesting to see just how long the irrational notion of what is for girls and what is for boys has been with us.