The Commodore 1351 is a mouse made by Commodore in 1986, which can be directly plugged into the 9-pin control port of a Commodore 64 or 128.
The Commodore 1351 is similar in appearance to the mouse supplied with Commodore Amiga computers of the time, but the two are not mutually compatible. In its default mode, it is a true proportional mouse, but by holding down the right mouse button when powering up the machine, it can be made to emulate a joystick.
The mouse was distributed with a user manual containing maintenance instructions, pinouts, and sample BASIC and machine language programs for the Commodore 64 and 128. Also included was a diskette containing diagnostic tools, demos, drivers, and an upgrade for the GEOS operating system
Source: Wikipedia, "[en.wikipedia.org/wiki/Commodore_1351 Commodore 1351]", available under the CC-BY-SA License.