The nuchal ligament is a ligament located in the back of the neck that extends from the base of the skull to the upper back. It is found in most mammals, though many animals, aside from humans and ungulates like sheep and cattle, do not have a well-developed nuchal ligament.
The purpose of the nuchal ligament is to provide support and stability for the head while running. The nuchal ligament absorbs the shocks created by the body when running or doing other strenuous activities, so that these jolts are not transmitted to the head. The muscles in the upper back also connect to this ligament, allowing them to rotate around it.