are usually little developed. No caecum, except in
_Platanista_.

The first family, _Physeteridae_, is typified by the sperm-whale, and
characterized by the absence of functional teeth in the upper jaw; the
lower teeth being various, and often much reduced in number. Bones of
the skull raised so as to form an elevated prominence or crest behind
the nostrils. Pterygoid bones thick, produced backwards, meeting in
the middle line, and not involuted to form the outer wall of the
post-palatine air-sinuses, but simply hollowed on their outer side.
Transverse processes of the arches of the dorsal vertebrae, to which
the tubercles of the ribs are attached, ceasing abruptly near the end
of the series, and replaced by processes on the body at a lower level,
and serially homologous anteriorly with the heads of the ribs, and
posteriorly with the transverse processes of the lumbar vertebrae.
Costal cartilages not ossified.

The first group, or _Physeterinae_, includes the sperm-whale itself
and is characterized by the presence of a full series of lower teeth,
which are set in a groove in place of sockets, the groove being
imperfectly divided by partial septa, and the teeth held in place by
the strong, fibrous gum. No distinct lacrymal bone. Skull strikingly
asymmetrical in the region of the nasal apertures, in consequence of
the left opening greatly exceeding the right in size.

In the sperm-whale (_Physeter macrocephalus_) the upper teeth are
apparently of uncertain number, rudimentary and functionless, being
embedded in the gum. Lower jaw with from 20 to 25 teeth on each side,
stout, conical, recurved and pointed at the apex until they are worn,
without enamel. Upper surface of the skull concave; its posterior and
lateral edges raised into a very high and greatly compressed
semicircular crest or wall (fig. 2). Zygomatic processes of jugal
bones thick and massive. Muzzle greatly elongated, broad at the base,
and gradually tapering to the apex. Lower jaw exceedingly long and
narrow, the symphysis being more than half the length. Vertebrae: C 7,
D 11, L 8, Ca 24; total 50. Atlas, or first vertebra, free; all the
other cervical vertebrae united by their bodies and spines into a
single mass. Eleventh pair of ribs rudimentary. Head about one-third
the length of the body; very massive, high and truncated, and rather
compressed in front; owing its huge size and for