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THE ETHMOID AND
THE PNEUMATIC SINUSES.

THE ETHMOID.

The part of the nasal cavity lying rostrad to the ethmoid
is of most peculiar appearance (PL 20). In the typically formed
mammalian skull we find, as is well known, the two conchas,
naso- and maxillofurbinal, dividing the nasal cavity into the three
well-known nasal passages. In the Elephant this structure has
been modified; only two nasal passages are seen, a narrow dorsal
and a more spacious ventral one; the medial nasal passage
seems to be lacking. In the preceding part of this paper a detailed
statement has been made concerning the structure of the
naso- and maxilloturbinal, according to which the ventral nasal
passage in the Elephant corresponds to the ventral + the medial
nasal passage in Mammalia.

The ethmoid in the old Elephant Chang, which shall first
be described, is of imposing size. It is true that it is not clearly
seen in the sagittal section (PI. 38 fig. 1), this bone having its
greatest dimension in breadth. On the other hand, the preparation
delineated in PI. 38 fig. 3, in which all the ethmoturbinals have
been removed, most strikingly demonstrates what a large space
is occupied by the ethmoid.

The ethmoturbinals form a compact bulk in a caudally directed
, deep concavity, which appears in the Elephant much more
than in other Mammals as a special part of the nasal cavity, on
account of the modified direction of this latter. The concavity
is dorsally bordered by the lamina cribrosa, ventrally by the lamina
transversalis, and caudally ending in the excavated rostral
plane of the presphenoid.

The concavity for the turbinals in several respects displa}^
peculiar features: the lamina cribrosa is very large, 11 cm long,
pearshaped in outline, caudally narrow, but rostrad considerably
expanding in the part between the 1. and 2. endoturbinals, measuring
12 cm in transverse section where it is the broadest. Generally
the lamina cribrosa in Mammals is placed so as to have a
nasal and a caudal plane; in the Elephant this is partly modified:
in the caudal part, o: as far as from the 3. endoturbinal to the presphenoid
, the lamina cribrosa has a frontal position with a dorsal
plane to the brain, whilst the rostral part is raised. This shape and
direction of the lamina cribrosa correspond exactly with the bulbils
olfactorius which is placed ventrally to the lobus frontalis.
The ethmoid consequently is ventral to the brain, a position which
is most probably connected with the shortening of the basis cranii
and with the shape of the brain, the long and narrow lobus frontalis
. — Also the ventral wall, the lamina transversalis, has peculiar
features, extending obliquely in rostro-ventral, more pronouncedly
ventral direction, which results in the aperture of the concavity,
in which the turbinals are placed, opening much more widely into

the nasal cavity than in other Mammals, in which the lamina
transversalis has a frontal position. This wall is moreover shortened
, the 2. and 3. endoturbinals continuing ventrally on the lateral
wall of the nasal cavity, rostrad to the lamina transversalis
(PL 38 fig. 1).

If we look at the ethmoid of the sagittal section of a mammalian
skull, we get the distinct impression that the elements
of this bone, the olfactory folds and the basal lamellae, extend
rostrad. In the Elephant we get quite another impression: here
a turning in ventral direction has taken place. The olfactory folds
and the basal lamellae are ventrally directed, and this conception
is confirmed, when the olfactory folds and all secondary plaits are
removed, so that the lines of origin of the basal lamellae on the
lamina lateralis become visible (PL 38 fig. 3). The main direction
of these lines is ventral. Several of them make turns on the way,
but only caudally to the 4. endoturbinal they adopt a ventral and
somewhat rostral direction. This turning with consequent alteration
in the position of the olfactory folds and the basal lamellae is intimately
connected with the direction of the lamina cribrosa, as
also in other Mammalia (f. inst. Echidna, Edentates), in which the
caudal part of this plate is more or less frontally situated, the
olfactory folds and the basal lamellae have here a ventral direction.
In the Elephant the case is, however, somewhat different, as not
only the turbinals issuing from the frontally situated part of the
lamina cribrosa have this direction, but also all the others, that is
the dorsal turbinals, issuing from the rostral, arched part of the
lamina cribrosa. This is a consequence of the altered direction
of the nasal cavity of the Elephant. Generally the ethmoid or the
regio olfactoria is in direct continuation of the regio respiratoria,
whilst, as said above, the regio olfactoria in the Elephant appears
as a caudad bulging-out from the dorsad directed nasal cavity.
Possibly the position of the nasoturbinal is of some importance
in this respect, as it forms a sharp boundary to the regio olfactoria
. It is evidently a requirement for more room which has
effected this turning of the turbinals. This structure also serves
to explain another and very conspicuous feature in the ethmoid
of the Elephant. As we know, the olfactory fold on the second,
sometimes also on the third endoturbinal in numerous Mammalia
(Echidna, Marsupialia, Insectivora, Carnivora, some Rodents and
Ruminants) extends far forward in the nasal cavity, far off the
regio olfactoria. In this respect the ethmoid in the Elephant is
somewhat more like that of the Perissodactyles and of Sus, in so
far as the olfactory folds in these Mammals are so short that they
hardly rostrad surpass the regio olfactoria. The second endoturbinal
in the Elephant only extends a very short way forward in the