Oh yes, those wheaten whirls. We used to do heelwork to music together and she always had the showiest whirls. 
She was such a clever girl, really easy to train and a super fast learner.
My girl was 13 too and had been ill for a long time, we had the tumour excised, including bone removal twice, but it just kept coming back and by that time we knew she'd never cope with hemi-mandibulectomy (half jaw removal).
I spent much of the last fortnight sat under the kitchen table with her and on the last day it was deep snow, so I had to carry her to the vets on foot, wrapped in a blanket, sobbing all the way there. 
I couldn't go home afterwards, just kept wandering the streets and ended up breaking down in tears when a lovely old lady stopped to offer me a lift home. 
It still feels so raw and my old border collie x belgian shepherd girl, who by coincidence is also 13) is heading the same way at the moment. She's not quite there yet, but it's breaking my heart all over again watching her deteriorate. She was still behaving like a pup a month or so ago, but she's suddenly become old, thin and weak and her light is beginning to fade. Cancer is such an evil disease.
Hope your ds is ok and you manage to get some sleep tonight.