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119 The ethmoid and the pneumatic sinuses.

plane is increased both in size and strength and consequently also
in its staying power. At this comparison with corrugated iron we
should, however, notice the modification that the undulations of
the bony lamellae are more or less angular and expanding in-
fundibuliform towards the surface of the skull. These bony lamellae
however play another and very prominent part in the
forming of the sinuses. On their way towards the surface the
borders of an undulation coalesce, whereby a small funnel-shape
compartment arises, open at the bottom. This compartment is
continued farther on towards the surface with undulated walls,
and through another coalescing of the borders of the undulations
it is divided into still smaller compartments a. s. f. It further
should be stated that between the primary lamellae and also between
the undulations of one primary lamella still more of the
consolidating process is going on in the shape of rampant arches;
this is also a well known fact from the pneumatic sinuses in other
Mammalia, but in the Elephant these rampant arches are found
to be much more numerous and besides most varying in height,
as f. inst. in Elephant h where these arches vary in height from
2—3 cm right under the surface to the very high rampant lamellae
reaching from the surface down to 1—3 cm from the bottom
of the sinuses. In this way the sinuses are divided into the
numerous diminutive compartments.

Through the part of the large sinus which pneumatizes the
squamosal is running the meatus acusticus externus, which had
in Elephant h the length of 10 cm, in Chang a length of 24 cm.

In the Elephants Chang and h the lamina lateralis of the
ethmoid in several places — in Chang even in many places, 15
in all — may be described as follows: in the intervals between
the lines of origin of the basal lamellae there are some pit-shaped
or cup-shaped depressions, in most places only one depression
in one interval, in a few places in Chang several (2—4), the largest
of these depressions is large enough to hold a pea. Some of
these pits are rounded in circumference, others elongated; some
are distinctly outlined through a sharp margin in all their circuit,
others only partially outlined through such a margin, whilst the
remaining part of the circuit is smoothly coalescing with the lamina
lateralis; finally there are still others with a margin passing
smoothly in the surface of the lamina lateralis in its whole circumference
.

It cannot be denied that especially the openings of the well
defined grooves strikingly recall the openings of the pneumatic
sinuses; and in the cases where we have no clear view of the
bottom of the pit, if f. inst. it is extending rostrad or caudally
in below an adjacent basal lamella, we are surprised to find a
pit only a few mm in depth, where we had expected to find a
pneumatic sinus. It may be difficult in each separate case to
make a sharp distinction between the terms "pit" and "minimal
pneumatic sinus" — it is only a difference in degree. As already
discussed in the above, a sinus can be of considerable circumference
in one half of a skull, but in the other half so strongly
diminished in size that it must be designated as a "bulla", rising
from the bottom of another sinus; if we imagine such a bulla
further diminished it would be indicated as a pit or a cup. That
openings of several pneumatic sinuses may occur in the interval
between two basal lamellae is known from other Mammalia with
well developed pneumatic systems. There is no doubt that these
pits are rudimentary pneumatic sinuses, checked in their growth
by adjacent sinuses.

To be sure: the ethmoid plays a prominent part in the Elephant
as to a luxurious development of pneumatic sinuses.

Finally it ought to be mentioned that the 8. and 9. ectotur-
binals in the Elephant Chang extend upwards into a pneumatic
sinus (see the textfigure), which could not be examined in details,
because the skull should remain preserved. That a turbinal can
extend into such a sinus is besides known from f. inst. in Canis
and Equus.

In the pars faciei the sinuses do not by far obtain as enormous
a depth as in the pars cerebralis; they are the deepest in
the caudal part of the intermaxillary, the maxillary and the nasal
bones. The „facial" sinuses are also divided into smaller compartments
, still relatively larger than in the ,,cerebral" sinuses,
and the division is carried out, as in the sinuses of other Mam-

The pneumatic sinuses. 120

malia, simply through septa extending from floor to ceiling or
through arches reaching from the wall to the ceiling. It was not
possible, not even in the largest of these sinuses, f. inst. the sinus
maxillaris in the Elephant h, to detect any system in this consolidating
process.

The sinus maxillaris as usual has its opening at the rostral
border of the lamina lateralis of the ethmoid, between this latter
and the downwards pointing process of the nasoturbinal. In Elephant
c this sinus is already of rather considerable extension; the
greater part of the sinus lies in the corpus of the maxillary, where it
reaches right down to the alveoli, and from here it extends partly
to the dorsal plane of the pars faciei, in the region before the
orbit, partly caudally into the pars orbitalis of the frontal, where
it borders on the rostral sinuses of the ethmoidal system. It also
projects into the processus zygomaticus, where it completely surrounds
the canalis infraorbitalis, o: this canal as usual runs through
the sinus. Finally it also expands into the hard palate, but is
here only of small circumference. In the Elephant h the sinus
maxillaris has become extremely large. In the corpus of the
maxillary it forms a high and long sinus reaching right down to
the alveoli and being divided into many rather large compartments
; dorsally in the pars faciei it forms large and deep compartments
, in the proc. zygomaticus enclosing the canalis infraorbitalis
; in the hard palate where it is also multicamerate it
extends almost to the end of the palate, measuring 8 cm where
it is the highest. But what is further contributing to the enormous
extension of this sinus is the fact that it also expands into
the pars dentalis of the intermaxillary where it has supplanted
the sinus intermaxillaris inferior in Elephant c. This intermaxillary
part of the sinus, which is divided into few large compartments
, is very large, long and increasing in depth caudally where
it measures 14 cm; it ceases at a considerable distance (8 cm)
from the anterior border of the intermaxillary. In Elephant e
the sinus, on the contrary, extends forwards even to the anterior
border of this bone; consequently the anterior marginal region
in Elephant h has grown much further in length than has the
sinus. In the last named Elephant the alveolus is strongly curving
forwards in the lateral part of the sinus. Finally the frontal
part of the sinus maxillaris in the median wall of the orbit has
become considerably larger than in Elephant c.

There are still some sinuses present which are specific to
the Elephant. Among these the constantly occurring sinus nasalis
ought to be mentioned the first; it is found in all the skulls we
have had at our disposal, also in Elephas africanus. On the ventral
plane of the nasal bone, at the bottom of the diverticle, mentioned
p. 103, and closely adjacent to the suture between this bone
and the pars ascendens of the intermaxillary, there is an enormous
opening (PL 26 fig. 2) almost oval in shape, often somewhat slanting
; in Elephant Chang it measures 6£ cm in height and is 5 cm
where it is the broadest. In Elephas africanus the aperture is also
large although not so enormous as in Elephas indicus. The aperture
opens into a rather large and especially high sinus (in Chang
21 cm high), which pneumatizes the whole of the nasal and a
smaller adjacent part of the frontal bone. Besides the particular
and unusual locality from which the sinus has developed we must
call the attention to the aperture being of gigantic size in comparison
with the openings of the other pneumatic sinuses. It is
difficult to determine the significance hereof, but the great size of
the aperture may at any rate give rise to stronger ventilation. It
may also be imagined, that by means of this large aperture the
skull might better serve as a sound-board to the well-known roaring
of the Elephant, mentioned in the preceding section of this work.
The position of the aperture particularly favours this notion, as
the powerful expiratory air current must also be led laterally to
the cartilaginous part of the nasoturbinal and thus right into the
sinus.

Further we find in the Elephant c the two intermaxillary sinuses
. The sinus intermaxillaris superior is of only small extension
in the pars ascendens of the intermaxillary, but it has an
opening which is almost as large as the opening of the sinus nasalis
. The openings are closely adjacent, only separated by a sharp
projecting margin. In Elephant Chang the two openings are of
equal size. From the material at hand of skulls of Elephas indicus