courbet's art, like his life, did decline in exile. one of the best pictures here, ''fox in the snow,'' is from around 1860, hardly late in courbet's life. it shows a landscape built up by layers of pigment as solid and packed as the snow. as often with him, there is the evocation of muffled air: the air as something tangible and unchanging, like stone. this is not pretty painting. it's a brutish picture, a wounded animal starkly silhouetted, painted with a sensuous concentration that seems almost akin to love.