The ligamentum nuchae lies near the dorsal surface of the neck, connecting the occiput to the thoracic neural spines and helping to support the head. It consists largely of elastin, a protein with rubber-like elastic properties. Experiments have been performed on deer, a sheep and a camel to measure the elastic strain in the ligament, both when the head is raised and when it is lowered as in feeding from the ground. The elastic properties of the excised ligament were investigated so that the forces in it, in the intact animal, could be inferred from the observed strains. The forces required to support the head have been calculated, and are compared with the forces inferred from the strains.