plates, directly above the nasal septum, are separated from each other by a rough
groove continuous with the lower roughened surface of the mesethmoid ridge, to
which the cartilage of that bone is attached and which is prolonged forwards
chiefly between the premaxillse to the extremity of the snout. The nasal plate
is thin and slightly expanded from above downwards, ending below in a free
sharp margin. A deep triangular anterior longitudinal notch separates the- wings
from the vertical plates, but both are closely applied to the premaxillse and
maxillse. At the upper margin of the wings, anterior to the nasal septum, they
are separated by an oval nodose rough surface, which is prolonged downwards
and forwards between the free extremities of the wings, and to it the mesethmoid
cartilage is also attached.
Palatine (PI. XL, fig. 12, and fig. 17 n).—The peculiar position of this bone
in Platcmista was first pointed out by Eschricht. I t appears in the anterior and
outer walls of the nasal cavities, and is placed so high in them that its upper
extremity rises above the low anterior border of the external nares in the dried
skull, the lower half of its nasal surface forming the anterior, and its upper half
the external wall of the nasal cavity. The former completes the canal, but is seen
with difficulty, owing to the backward projection of the pterygoids. When the
TnflTilla. is separated from the skull, the palatal is seen to invest the greater part
of its posterior and external borders, below the frontal plate and the inferior
border of the vomeric crest of the maxilla. I t is nearly vertical, but has a
slightly downward and forward course. Viewed from the outer side, it is seen
to form the posterior boundary of a large round foramen in the maxilla, the
inward and forward continuation of the pterygo-maxillary fissure. The lower
border of this foramen is defined by a strong longitudinal lamellar process, the
backward continuation of the external plate of the maxilla, which also forms
the lower outer wall of the pterygo-maxillary fissure externally. This process terminates
abruptly on a line with the posterior margin of the large foramen, and
its root is so deeply grooved and so firmly embraced by a notch about the middle of
the vertical height of the palatal (the two are clasped together like a hook and eye),
that they can only be separated by fracture. The notch divides the palatal into two
external surfaces, a superior and inferior; these form a very obtuse angle with
each other, the former being directed upwards and inwards and the latter downwards
and inwards, due to the spirally curved character of the nasal surface. The upper
surface is also slightly bent from before backwards and inwards, and the inferior portion,
which is concave from without inwards, has its posterior margin a little outwardly
curved. The former has its upper extremity abruptly truncated and somewhat
concave where it embraces the inferior extremity of the external surface of the
frontal plate, of the maxilla. The inferior portion has a pointed extremity which
reaches close to the lower margin of the posterior angle of the vomerine crest of the
maxilla, so that it is only excluded from appearing on the middle of the palatine
surface by a few lines, and is directly below the pterygo-maxillary fissure. The
whole of the lower and one-half of the superior surface are completely hidden by
the pterygoid, the only portion which is not so invested being the upper half of
the superior division of the external surface. The latter lies in a vacuity defined by
the orbito-sphenoid, frontal, maxillary, palatine, and pterygoid, and corresponds to
the spheno-maxillary fossa, because the sphenoidal fissure and optic foramen open
into it. Close to its anterior margin, behind the large maxillary foramen already
mentioned, there is a thin small outwardly-projecting plate, perforated on its upper
surface by a minute foramen. A bristle passed downwards and forwards through
this appears at the middle of the anterior border of its lower half ; but when the
pterygoid is in position, the tract in question is lengthened above and below by the
opposition of the pterygoid to the outer surface of the bone. The canal is thus
defined by the pterygoid, palatine and maxillary, and is the pterygo-palatine canal.
An imperfection of ossification exists in the nasal surface of the bone and leads
into the canal, doubtless transmitting a nerve to the mucous surface of the nasal
canal. Immediately above this foramen there is another which leads directly into
the nasal canal. The inner surface of the palatine, which is much more limited in
its extent than the external, is applied by its upper half to a narrow surface on the
hinder end of the maxilla below the frontal plate of that bone, fig, 17 n, and its lower
fra,If to the outside of the vomerine crest of the maxilla. The centre is thin and
marked by numerous imperfections of ossification, while its nasal borders are thickened
and the external slightly expanded. A thin plate projects forwards from the upper
portion of the anterior border t>f the bone at right angles to its long axis and
corresponds to the anterior half of the concavely-truncated upper external border
which embraces the base of the frontal plate of the maxilla. The lower half of the
internal surface is smooth and slightly convex.
The nasal aspect of its posterior surface is smooth, but porous, being covered
with numerous minute foramina. By far the greater portion of the upper half
looks inwards, but a small part enters into the anterior wall of the nasal canal,
while its lower half is directed inwards and backwards. In looking into the nasal
cavity from below upwards, it is seen articulating by its inner or anterior margin
with the side of the rough triangular expansion of the vomer, anterior to its nasal
septum, and above this through the whole of its nasal course with the nasal surface
of the posterior extremity of the maxilla. Its external or posterior border, on
the other hand, is observed to lie along the anterior margin of the nasal surface
of the pterygoids, at the upper end of which the external margin of the wing
of the vomer is wedged in between it and the pterygoid, the remainder of the
margin being applied to the former. Its upper margin is in contact with a
transverse ridge on the anterior surface of the frontal immediately external to
the mesethmoid, and its external angle articulates with that bone. In this
portion of its course it lies between the mesethmoid and vomer, the frontal,
maxillary, and pterygoid, and is above the level of the orbit, but far removed from
it posteriorly.
Malar (PI. XL., figs. 15 and 16).—This is a relatively small bone consisting, as
in Cetacea generally, of two portions, a round thick knob-like anterior, and a styli