At type of frame
used in some cars.
The backbone frame was made famous by Colin Chapman who used it in the Lotus Elan. This frame has the cross-section of a rectangular box, that runs along the center portion of the vehicle and occupies the space between the seats. This box will usually divide at the front, then run along either side of the transmission and engine, eventually meeting up with a crossmember to which the front suspension is mounted. A similar triangular frame encloses the final drive housing at the rear of the vehicle, (and of course the rear suspension is attached to this).
This frame design combines a light weight with a high degree of torsional rigidity, making it excellent for sports cars.