This is an image of nerves, the nerves of a dog, a new-born dog.
“Clarke’s column” is also called the posterior thoracic nucleus, a part of the spinal column. The main thing it does is control proprioception, the “sixth sense” that tells us where our body parts are relative to each other even when you can’t see or feel anything.
This image comes from The nervous system of vertebrates by John Black Johnston, which I found in the Biodiversity Heritage Library.