where did ``xxx" quotes come from?

Ive seen the quoting style of using 2 backticks (``) in front with regular double quotes on the end of something being quoted. Im assuming this is from K&R, but does anyone know where that originates from and if there is any practical reason for it?

^{66669966669999666666999966999966666699666699999966669999669999}recursive_quotes^{66669966669999666666999966999999666699666699999966669999669999}