The main external parts of a manual transmission are the clutch and the gearbox. In a traditional gearbox, the gears are arranged in a logical fashion: first and second gear across from each other, third and fourth gear across from each other and fifth gear and reverse across from each other. This enables the driver to switch fairly easily between consecutive gears, especially between the often-used first and second gears.
A dog gearbox, also called a dog leg gearbox, is arranged somewhat differently. Although the gears are still placed in a logical order, the reverse gear is located across from first gear instead of across from fifth gear. Therefore, it is easier to switch between second and third gear, but more difficult to switch between first and second gear. In fact, it is the method of switching between first and second gear that gives the gearbox its name. The up-and-over movement required to make this switch resembles the shape of a dog's hind leg.
The dog gearbox is often used in race cars. In road racing, drivers use the first gear very rarely--only at the start of a race, as necessary. Therefore, it is advantageous for a driver to be able to switch easily between the second and third gears, whereas the more difficult maneuver to switch between first and second gears is not seen as a disadvantage.
