The thoracic spine and sacrum have a kyphosis, or backward convex curve. (physiologicnyc.com)
The cervical and lumbar spine have a lordosis, or forward convex curve. (physiologicnyc.com)
Woelffer's paintings from this period began using invented symbolism, motifs such as handprints, flag - like stripes, and a shape he called a «mirror» — two convex curves reflecting across a central axis. (thelandinggallery.com)