enormously-developed supra-occipital in the adult. Here again the Zeuglodonts are more typically Mammalian, for in them the parietals have a normal development and situation, rising even into a median crest as in so many quadrupeds. The bones related to the organ of hearing, the tympanis and petrous bones, are very solid and dense in structure. Moreover they are but loosely attached to surrounding bones, and are thus easily and frequently lost. Nearly the only mammals which resemble the Whales in the fact that the pterygoids sometimes meet in the middle line below are the Edentata (Anteater and Armadillo, see p. [167]). But in both groups this peculiarity is not universal.
Fig. 185.—A section of a skull of a young Caa'ing Whale (Globicephalus melas). × 1⁄5. a, Angle; an, anterior nares; AS, alisphenoid; bh, basihyal; BO, basioccipital; BS, basispnenoid; cd, condyle; cp, coronoid process; ExO, exoccipital; Fr, frontal; id, inferior dental canal; IP, interparietal; ME, ossified portion of the mesethmoid; Mx, maxilla; Na, nasal; Pa, parietal; Per, periotic; Pl, palatine; PMx, premaxilla; pn, posterior nares; PS, presphenoid; Pt, pterygoid; s, symphysis of mandible; sh, stylohyal; SO, supra-occipital; Sq, squamosal; th, thyrohyal; Vo, vomer. (From Flower's Osteology.)
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
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
-shaped chevron bones below.
Fig. 186.—Section through middle line of united cervical vertebrae of Greenland Right Whale (Balaena mysticetus). × 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.)
