elongated character of the symphysis which, in adult females, forms nearly two-
thirds of the lower jaw, whereas in males it constitutes only a little more than one-
half of the total length of the mandible. The rami become united at the symphysis in
utero. Only one tooth in the young cannot he said to he symphysial, whereas in adnlts
with all their teeth intact the last tooth lies in debatable ground. In the young,
the symphysial portion is slightly curved upwards and forwards as far as the twenty-
third tooth from the first, and then forwards and downwards, there being a faint
upward curve at the base of the fourth tooth. The symphysial, or internal alveolar
plate is but slightly curved in the young skull, thus agreeing with the nearly
straight maxilla; hut, as age advances and the curves become more intensely marked,
it also partakes in the general curvature, which is adapted to the opposed curves of
the maxilla. This curvature is a means, in addition to the interlocking of the teeth,
by which the upper and lower halves of this long snout are held firmly in position
when the month is closed.
The symphysial dental portion is strongly laterally compressed, the two
alveolar lines being in dose apposition. ■ The external surface is slightly concave,
and the middle of the symphysis is deeper than at the beginning of the ramus
and much more so than at its own terminal upturned distal third. The coronoid is
moderately high and arched, the depth of the jaw through it being less than one.
half of the distance between the condyle and the posterior end of the symphysis.
I t is concave at its base externally and flat internally, and its posterior margin
slopes down to the condyle, which is vertically oval and directed backwards.
The under surface of the coronoid portion of the ramus is broad, by the inward
extension of the. inner margin as a thin slightly outwardly curved plate, producing
a concavity which is continuous with the fossa along the side of the lower border
of the symphysis. A short sharp longitudinal ridge for the attachment of the
external pterygoid muscle occurs in the concavity of the ramus before the condyle.
The opening to the dental foramen, on the inner side of the jaw, .is large and prolonged
backwards into the lower angle of the condyle, from the outer surface of
which it is only separated by the thickness of the condylar plate itself. In adult
skulls, this becomes partially absorbed, so that the two communicate. The dental
canal is very wide and mfundibuliform.
The lower jaw partakes of the general asymmetry of the skull, the symphysial
portion being twisted to the left side from its base forwards, and the free portion of
the rami differing in their curves, the left being more externally curved than the
right. ■ ,
Syoid (PI. XL, fig. 20).—The basihyal (IK) is a somewhat transversely crescentic
flattened bone with a convex anterior and a concave posterior border, and
slightly concave on its upper and under surfaces, the two extremities of the crescent
being abruptly truncated. I t is. not anohylosed to the thyrohyals ( th ) which are
slightly curved, dilated at their basihyal ends, and contracted externally to that,
with a prominent nodosity in adult life on their anterior surfaces defining the
contraction. The ceratohyal is a long cartilaginous rod, nearly as long as the
.stylohyal (sh), which is more or less cylindrical and twice curved on itself and
somewhat compressed at its cranial end. In the foetus, the basihyal is a minute
ossicle, whereas the thyro and stylohyals are well ossified.
Vertebral column (PL XXXIX).—The vertebral formula is this: C 7, D 10
or 11, L 7 or 8, C 26 or 27 = 51 or 52. I have examined twenty perfect skeletons
and have never found less than fifty-one vertebras.
Characters.—The vertebral column (figs. 3 and 4) describes two curves; the
six anterior cervical vertebra having a slight upward bend,' while the dorsal
vertebra from the last to the seventh have an upward and forward curve, Whereas
from the latter to the first, the direction is downwards and forwards. The
lumbar and caudal vertebrae are nearly in a straight line', the terminal seven vertebra
being slightly curved downwards. The cervical vertebra are all distinct.
The centra of the vertebra are rather narrow antero-postenorly, their breadth
being considerably in excess of their length, in any portion of. the column. The
strongly developed spinous processes are directed backwards in the anterior vertebra,
up to .the fifth dorsal; the process of the next vertebra is erect, whilst all the
processes of the succeeding vertebra are curved forwards in a marked degree, and
the processes entirely disappear in the fortieth segment. The neural canal, which
is capacious in the cervical and first part of the dorsal region, being much broader
than high, rapidly diminishes in capacity, its breadth in the last dorsal vertebra
being one-half of what it is in the first rib-bearing segment. In the lumbar region
the height gradually exceeds the breadth. In the tenth caudal it is reduced to
a tube about one line and a half in diameter. The strongly-developed metapophyses
first appear in the fifth dorsal, and can be traced backwards as far as the fourteenth
caudal, and are another marked feature of this dolphin. The last trace of zygapo.
physes occurs on the sixth lumbar vertebra. Transverse processes are present
from the atlas to the fifteenth caudal in a more or less decided manner, but they
are especially strongly developed in the lumbar and first five or six caudal vertebra.
S p e c i a l characters o f mdimdual vertebra.—The atlas is much broader than
high, and has a strong transverse process, which is directed backwards and out.
wards. It springs from the pedicle external to the outer border of the posterior
zygapophysis, and from between it and the anterior zygapophysis, i.e., above what
would he the position of the neurocentral suture; it would thus appear to be
serially homologous with the superior transverse process of the vertebra immediately
behind it. The inferior transverse process is most intensely developed in the sixth
cervical vertebra, where it is directed forwards and outwards, and it can he distinctly
traced forwards to the fourth cervical, here springing directly from the side of the
centrum, but its superior root originating from , the inferior root of the superior
process. As there can be but little doubt that the transverse process of • the axis is
serially homologous with the superior transverse process behind it, the process of
the atlas which occupies a relatively higher point on the neural arch, and which
follows the direction common to the two superior transverse processes behind it,
is also the homologue -of these processes, The neural arch is lower and more
T 3