Why is a pony cylinder used in scuba diving called a pony

Question

Why is a pony cylinder used in scuba diving called a pony

Answer 1

******These "pony" cylinders are simply named as such since they are physically smaller than normal tanks which one would attach to a Buoyancy Control Device.  There are numerous uses for such cylinders.  They are awesome for emergency back-up air supply, and are also used as a reserve supply for extended decompression times.