the Mother in Law seat, there were a couple versions, but they mostly were exposed to the weather and not equipped to keep someone seated in an emergency braking event

This simply takes top honors for the the most spiteful mother in law seat ever made! A 1910 Welch

There was this variety that slid out from the side, and I've seen it on the Kissel and and the Paige Model 6-55 Daytona Speedster

and there was this flip lid on this 1911 Olds Autocrat

https://justacarguy.blogspot.com/2017/08/1911-olds-autocrat-has-cool-rumble-seat.html

the 1910 Matheson had one mounted to the spare tire /5th wheel

Paige Model 6-55 Daytona Speedster with mother in law seat

and the 1920 Kissel Gold Bug I posted back in 2013

https://justacarguy.blogspot.com/2013/04/1920-kissel-gold-bug-roadster.html

https://fornoob.com/the-mother-in-law-seat/

the great art and variety of design in 1909 car company catalogs

 The Corbin 4 Passenger baby tonneau

 Corbin 4 passenger roadster

Corbin 5 passenger touring

Aboev is a 1909 Corbin I found on http://theoldmotor.com/?p=19172

Notice in the above description the roadster is said to have a "mechanician's" seat. What the hell? I've learned a new word! According to Wikipedia a mechanician is an engineer or a scientist working in the field of mechanics, It is also the term by which makers of mechanical automata use in reference to their profession.

found among hundreds of great old car catalogs at http://digitalgallery.nypl.org/nypldigital/dgkeysearchresult.cfm?word=title_id_list:454055&slabel=Automobiles%253A%2520Manufacturers%2520catalogues%252E&sScope=images&sLevel=1