The vertebral column is remarkable for the fact that more or fewer of the cervical vertebrae may be fused together into a short and compact mass. This is seen at its maximum in the genera _Balaena_ and _Neobalaena_. The odontoid process of the second {352} vertebra, though hardly at all marked, is nevertheless really present and developed from a bony centre of its own, as in other mammals. The dorsal and lumbar vertebrae are, of course, to be distinguished by the presence of ribs attached to the former; but as there is only a rudimentary pelvis, not attached to the vertebral column, no sacral region can be detected. The caudal vertebrae are to be recognised by the [234]-shaped chevron bones below. [Illustration] FIG. 186.--Section through middle line of united cervical vertebrae of Greenland Right Whale (_Balaena mysticetus_). x 1/9. _a_, Articular surface for occipital condyle; _e_, epiphysis on posterior end of body of seventh cervical vertebra; _sn_, foramen in arch of atlas for first spinal nerve; 1, arch of atlas; 2, 3, 4, 5, 6, conjoined arches of the axis and four following vertebrae; 7, arch of seventh vertebra. (From Flower's _Osteology_.) [Illustration] FIG. 187.--A, Sternum of Greenland Right Whale (_Balaena mysticetus_). x 1/15. B, Sternum of Common Rorqual or Fin Whale (_Balaenoptera musculus_). x 1/10. (From Flower's _Osteology_.) The sternum in the Whale tribe is much more modified in the Whalebone Whales than in the Odontocetes. In the latter it is made up of several pieces, as in other mammals, which often, however, become coalesced. In the Mystacoceti this bone is a single piece, to which only one pair of ribs is attached, and its {353} form is characteristic of the genus. It is heart-shaped, more or less, in _Balaena_, and somewhat cross- or [235]-shaped in the genus _Balaenoptera_. In the Odontocetes the ribs have, some of them, the normal attachment by capitulum and tuberculum. In the Mystacocetes the attachment, where it exists, is very loose, and the tuberculum alone is attached to its vertebra. This allows of the freer play of the ribs during respiration. The scapula has a very characteristic form in these animals. The acromion, where it exists, is placed near the anterior margin of the shoulder blade, and overlaps the generally long coracoid process. Clavicles are totally absent. The pelvis is very rudimentary, consisting merely of a single bonelet, to which are attached the rudiments (in some cases) of a femur, and, in _Balaena_ (Fig. 188), of a tibia also. [Illustration] FIG. 188.--Side view of bones of posterior extremity of Greenland Right Whale (_Balaena mysticetus_). x 1/8. _i_, Ischium; _f_, femur; _t_, accessory ossicle representing the tibia. (After Eschricht and Reinhardt) (from Flower's _Osteology_.) Whales are to be divided into three great groups:--(1) the Whalebone Whales or Mystacoceti; (2) the Toothed Whales or Odontoceti; and (3) the entirely-extinct Archaeoceti or Zeuglodonts.