Please answer a question about the following article about Alps:

The highest portion of the range is divided by the glacial trough of the Rhone valley, with the Pennine Alps from Mont Blanc to the Matterhorn and Monte Rosa on the southern side, and the Bernese Alps on the northern. The peaks in the easterly portion of the range, in Austria and Slovenia, are smaller than those in the central and western portions.

The highest portion of the Alp's range is divided by what?
the glacial trough of the Rhone valley