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The ethmoid and the pneumatic sinuses.

The pneumatic sinuses.

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it appears that the sinus intermaxillaris superior is most variable.
Between the condition in Elephant c and the complete reduction
of this sinus in Elephant h there are transitory stages: the limitation
of the aperture may be less well-marked, especially in dorsolateral
direction, and the sinus may be reduced so that at last
only a feeble groove-shape depression is to be found on the pars
ascendens of the intermaxillary, directly laterally to the aperture
of the sinus nasalis. — In Elephas africanus we meet with the following
conditions: in x there is in each of the two halves a large
aperture, which it is of the same size as the aperture of the sinus
nasalis and closely adjacent to it. The aperture of the sinus
intermaxillaris sup. is, however, not sharply outlined dorsally.
In y there are 4 apertures in the right side, 3 on the left side
of the pars ascendens of the intermaxillary, on each side arranged
in a row, with the medial aperture close to that of the sinus nasalis.
The apertures are rather large, a couple on each side being so
large that a little finger may be introduced in them, but, for all
that, none of them can in size compete with the apertures in x
and in Elephas indicus. In z there are in the right half 2 elongated
, rather broad apertures, just laterally to the aperture of the
sinus nasalis, and a little more dorsally there are 2 small apertures
(J cm broad); in the left half there is only 1 rather large,
irregular aperture.

The sinus intermaxillaris inferior has its relatively large aperture
(1^ cm high, \ cm broad in Elephant c) on the lateral wall
of the nasal cavity, nasally in the ridge-shaped depression. This
sinus is in Elephant c of rather considerable circumference in the
intermaxillary, especially in the pars dentalis; in its lateral part

the alveolus curves forwards. In Elephant h it is completely
reduced and its place has been occupied by the sinus maxil-
laris.

Finally we have to discuss the pneumatizing of the nasal part
of the nasoturbinal (the caudal part is pneumatized by the ethmoidal
system). This pneumatizing process is partly executed by
a sinus from the ethmoidal system (in the Elephant c), but is
besides due to some particular, small sinuses appearing in varying
numbers, and the apertures of which are placed on the lateral
wall of the nasal cavity, partly laterally, partly and especially ven-
trally to the nasoturbinal, i. e. on the wall of the median meatus.
The presence of similar apertures, which have been proved through
probing to lead into the nasoturbinal, has also been stated in other
skulls which have been sawed through, such as Elephant h (see
description), g, in which there are 2 apertures in the right and
3 in the left half, Chang, 1 aperture in the right halt (PI. 27 fig. 3
and PI. 31 fig. 5), and finally in the skull of x, in which 1 aperture
is found in the right half, 2 in the left.

The middle nasal passage in the Elephant has altogether a
pronounced tendency to the formation of sinuses — besides the
two constant, the sinus nasalis and the sinus maxillaris — what
is not common in Mammalia; it is best known in the Perisso-
dactyla, in which however only one, the sinus malaris, is formed
besides the sinus maxillaris. This „nasal" pneumatizing in the
Elephant is, like the „ethmoidal", distinguished by a great variation
; even sinuses which in one specimen is of considerable
extension may in another, resp. on the other side of the same
individual, become completely reduced.