Figure 1.—Sacrum of "Apatosaurus ajax" Marsh; seen from below. one-tenth natural size, a. first sacral vertebra; b. transverse process of first vertebra ; c. transverse processes of second vertebra; d. transverse process of third vertebra; /. foramen between first and second transverse processes; /•'. foramen between second and third processes; p. last sacral vertebra; g. surface for union with ilium.