Above you will see several texts which, when clicked, show the respective pictures. Apart from the last one, all the pictures show an Audi all-wheel drive. The first two pictures are of a somewhat older, mass produced Quattro-drive, each having an in-line engine, found, at that time, in the Coupe of the same name.
With these gearboxes the torque is transferred by a hollow shaft from the center differential to the front axle. You can find a more precise description here. However, it is more important that the axle drive lies between the clutch and the gearbox. This is the way it has almost always been with the straight, front mounted engine and front-wheel drive, and with the straight, mid-mounted engine and rear-wheel drive.
Because the drive bevel gear in the axle drive meshes with a relatively large crown-wheel, this must be offset at an angle of 90°, a lot of space is needed between the engine and the gearbox for the axle drive. This would perhaps, not be so bad, if the straight mounted engines didn't already make the vehicles front- or rear heavy with the respective disadvantages for the road-holding.
The solution was always there, it's shown in picture 3. In this case, an automatic gearbox transfers the torque to the axle drive. Because in this type of gearbox, the return-feed to the front must occur around the outside, the axle drive is found next to the gearbox, i.e., in the picture, behind it. Unfortunately, this doesn't save any space at all, because the, mostly optional automatic gearbox has to be fitted into the space provided for the manual box.
It really becomes interesting in picture 4. Here you can see (at the top of the picture) the axle drive lying next to the gearbox in the top-view. In contrast to picture 3, the available space is much more effectively used. The two flanges for the drive shafts have been moved in the direction of the engine, which clearly reduces the front-, or rear-end overhang.
Picture 5 illustrates it even better, because it presents a cut-open view of the gearbox and the axle drive. The axle drive, with it's large crown-wheel, is moved to the outside and the clutch and gearbox are much closer to each other. So that the two drive shafts are the same length, the flange on the other side is pulled further out, which can easily be seen in picture 4.
In picture 6 you can see that the manual gearbox adapts the same construction method. Although the one shown here is automated with a double-clutch, the arrangement corresponds to that of the manual gearbox. Since this fundamental change, e.g., Audi and Porsche have a longer wheelbase without the overall length being increased. In both of them the engine overhang is reduced, and the center of gravity is shifted more to the middle. 03/12