e_ (see DOLPHIN).

The last family of existing cetaceans is the above-mentioned
_Delphinidae_, which includes the true dolphins, porpoises, grampuses
and their relatives. As a rule there are numerous teeth in both jaws;
and the pterygoid bones of the skull are short, thin and involuted to
form with a process of the palate bone the outer wall of the
post-palatine air-sinus. Symphysis of lower jaw short, or moderate,
never exceeding one-third the length of the jaw. Lacrymal bone not
distinct from the jugal. Transverse processes of the dorsal vertebrae
gradually transferred from the arches to the bodies of the vertebrae
without any sudden break, and becoming posteriorly continuous serially
with the transverse processes of the lumbar vertebrae. Anterior ribs
attached to the transverse process by the tubercle, and to the body of
the vertebra by the head; the latter attachment lost in the posterior
ribs. Sternal ribs ossified. The blow-hole is transverse, crescentic,
with the horns of the crescent pointing forwards.

First on the long list is the narwhal, _Monodon monoceros_, in which,
apart from some irregular rudimentary teeth, the dentition is reduced
to a single pair of teeth which lie horizontally in the maxilla, and
in the female remain permanently concealed within the socket, so that
this sex is practically toothless, while in the male (fig. 8), the
right tooth usually remains similarly concealed while the left is
immensely developed, attaining a length equal to more than half that
of the entire animal, projecting horizontally from the head in the
form of a cylindrical, or slightly tapering, pointed tusk, without
enamel, and with the surface marked by spiral grooves and ridges,
running in a sinistral direction. Vertebrae: C 7, D 11, L 6, Ca 26;
total 50. Cervical region comparatively long, and all the vertebrae
distinct, or with irregular unions towards the middle of the series,
the atlas and axis being usually free. Flipper small, short and broad,
with the second and third digits nearly equal, the fourth slightly
shorter. No dorsal fin. See NARWHAL.

[Illustration: FIG. 8.--Upper surface of the Skull of male Narwhal
(_Monodon monoceros_), with the whole of both teeth exposed by removal
of the upper wall of their alveolar cavities.]

Closely allied is the beluga or white-whale (_Delphinapterus leucas_),
of the Arctic seas, in which, however, the