Fig. 4. A in Novel pneumatic features in the ribs of the sauropod dinosaur Brachiosaurus altithorax

Fig. 4. A cervical rib of sauropod dinosaur Apatosaurus ajax Marsh, 1877 (specimen number unknown), as illustrated by Marsh (1896: figs. 7, 8), including the original caption. Note the "posterior process" marked as "r" in the illustration. This is probably the "second tubercle" referred to by Riggs (1901: 549, 1903: 303, 1904: 239), which he considered some part of one or more of the Brachiosaurus ribs to be homologous with.