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115

The ethmoid and the pneumatic sinuses.

The pneumatic sinuses.

116

partments arise. In the 2. and 3. lamellae (PL 42 fig. 1) the sinus
extends into the radical part of the lamella, which thus becomes
vesicularly expanded, 3—4 cm thick.

The sinus 9' and the sinus 10' are two quite small sinuses
in the ventral part of the frontale (pars orbitalis); they are not
visible in PI. 44 fig. 1, as they are hidden by the strongly projecting
crista orbito-temporalis.

The sinus 13' is a little narrow sinus in the frontale, completely
covered by the sinus 4'.

The sinus 14-', lying in the frontale (pars orbitalis), is so small
that it is hidden by the crista orbito-temporalis.

The sinus 15' is a rather large, very irregular sinus in the
frontale (pars orbitalis); rostrad it winds in between the sinus 4'
and the sinus maxillaris.

The sinus 16' is a small sinus in the frontale (pars orbitalis),
completely covered by the preceding.

The sinus 19' is a small bulla arching into the sinus 15' without
reaching to the surface.

The sinus 20' is small, narrow and irregular, lies in the frontale
(pars orbitalis) ventrally to sinus 15'.

Between the basal lamellae of the 2. endo- and the 23. ecto-
turbinal there are 3 apertures; the dorsal one close below the
lamina cribrosa leading into a small irregular sinus If, which
lies quite ventrally in the frontal bone, projecting downwards
into the maxillary, where it extends even to the alveolus. The
two other apertures lead respectively into sinus IIa and sinus lib',
both of which are quite small; they lie ventrally in the frontale,
caudally to the sinus IF and are hidden by the crista orbito-
temporalis.

The sinus 23', which is quite small, is completely covered by
the ventrorostral part of the sinus 8'. The sinus 23 a is a little
larger and extends downwards into the maxillary to the alveolus,
caudally to the sinus II'.

The sinus III' is a very small sinus in the dorso-lateral part
of the presphenoid, completely covered by the sinus 8'.

The sinus 25' is a rather broad, but low sinus in the dorsal
part of the presphenoid.

The sinus 26' is a rather large sinus, divided into several small
compartments, lying in the rostro-dorsal part of the presphenoid,
where it reaches upwards to the foramen opticum.

The sinus 26a is a rather large irregular sinus in the basi-
sphenoid extending from here into the basioccipitale, where it
reaches almost to the middle; caudally to this point a sinus from
the right half of the skull expands into the basioccipitale, pneumati-
zing it as far as to 2\ cm from the border of foramen magnum.

The sinus V is a bulla, a little larger than a pea, arching into
the sinus 26'.

The sinus Va. In the rostro-ventral part of the presphenoid
a sinus extends from the right to the left side; caudally to that
the sinus V a' is lying, it is somewhat broad, but low and divided
into several small compartments; it lies in the presphenoid.

The sinus Vf is a relatively large sinus in the dorsal part of
the presphenoid, caudally to the preceding sinus; it expands laterally
beneath the sinus 25'.

Besides the above mentioned sinuses there are on the lamina
lateralis of the ethmoid at the 15., 16., 17. and 20. ectoturbinals
and at the 2. and 3. endoturbinals groove-shaped depressions of
different sizes, and with more or less distinctly outlined apertures,
in likeness with those mentioned in Chang.

On the lateral wall of the nasal cavity a furrow-like depression
like the one mentioned in Elephant c is found, the furrow is only
broader in h. Caudally in this furrow there is a large aperture
leading into the sinus maxillaris. This sinus has obtained a very
considerable extent, relatively far larger than in c. Through the
aperture it is in communication with the part of the sinus lying
in the maxillary bone, in the part above the alveolus, and is divided
into many relatively large compartments. The sinus extends
into the proc. zygomaticus, where it encloses the canalis infra-
orbitalis, at the same time projecting into the hard palate which
it pneumatizes in almost its whole length, also here through the
formation of rather large compartments; in the highest place the
palate is 8 cm thick. Rostrad from this ventral part of the sinus
maxillaris two prolongations are sent out, a lateral and a median

one between which the sinus 4' is wedged in. The lateral prolongation
extends dorsally upwards into the rest of the maxillare
with few but rather large compartments, whilst the median one
expands into the intermaxillare, pneumatizing the greater part of
this bone by means of large and irregular compartments; into
the lateral part the alveolus of the incisor tooth is strongly arching.
The sinus maxillaris here occupies a space which is in Elephant c
pneumatized by the sinus intermaxillaris inferior; this sinus is completely
missing in h.

As already mentioned the sinus intermaxillaris superior as well
as inferior are completely reduced; their places are occupied by
other sinuses (see above).

The sinus nasalis. On the ventral plane of the nasal bone
in close vicinity of the suture between this bone and the intermaxillare
is found an enormous aperture, obliquely pear-shaped,
1\ cm in height and 5 cm in maximum breadth. It is in continuity
with a large sinus in the nasal bone and in the adjacent
median part of the frontale, where it extends even unto the septum
sinuum and is 15 cm in height; caudally it borders on the
sinus 6' and laterally on the sinus 4\ The sinus is divided into
several relatively large compartments. From the caudal end of
the sinus issues a diverticle-shape prolongation, 7 cm high, extending
caudally into the internal part of the frontale but not
reaching the septum; it is covered by the sinus 6', which is the
reason why this sinus has got its above mentioned particular shape.

The pneumatizing process issuing from the cavum tympani
is rather considerable. In the tympanicum proper only two very
small sinuses may be designated as "cellulae tympanicae"; the
other sinuses (there are 5 in all) have become relatively extensive
with extraordinarily large round apertures (1 cm broad).
From each sinus several evaginations issue with rather high lamellae
between them; the lamellae and intersinuous septa together
form a consolidating system radiating in rostrad direction from
the ventral plane of the tympanicum. Finally there is caudally
in the cavum tympani a large aperture leading into the sinus occipitalis
, a rather considerable sinus in the exoccipital bone. From
this sinus several evaginations radiate in dorsal and lateral direction
.

The pneumatic sinuses are so enormously developed in the
Elephant that no other Mammal can enter in comparison, and
they play a prominent part in the postembryonal metamorphosis
of the skull. Pneumatic sinuses are found in almost all bones,
with the only exception of the jugal bone, in which they are
missing.

The impression, conveyed by an inspection of the chiselled-up
skull of the Elephant h (PI. 28 fig. 2 and PI. 29 figs. 5 and 6), is
imposing, because of the large expansion of the sinuses, their enormous
depth, which is in several places so considerable that we
cannot see the bottom, and finally because of the great number
of mostly small compartments into which the sinuses are divided,
preventing us from detecting the boundaries of each separate sinus,
which is possible in other large Mammals (Rhinoceros, Bos). In
the Elephant we are also prevented from getting a survey of the
systems of consolidating lamellae which are always developed where
a pneumatic sinus obtains a certain depth; only in the occipital
plane (PI. 29 fig. 6) we get the impression of a radiation towards
the surface and are besides able to detect the wavy shape of the
bony lamellae. With the exception of the sinuses in the nasal and
intermaxillary bones, where the sutural planes form a septum sinuum
between the right and the left halves, no corresponding
septum is seen in the cerebral part of the skull, as it is in other
Mammals. Only in the young Elephant c, in which the sinuses
are still relatively low and more easily detected, this septum is
conspicuous (PI. 29 fig. 1; cp. PI. 43 fig. 3); it is here rather
considerably deviating, which is a well-known fact also in other
Mammals.

Already in the 3—4 years old Elephant c (PI. 28 fig. 1, PI. 29
figs. 1 and 2) the pneumaticity has become relatively extensive.
The dorsal wall is pneumatic, except for the rostral half of the
intermaxillaria. It is of special interest that in the rostral part
of this wall the sinuses are in the pars cerebralis already divided
into several small compartments, whilst in the caudal part and