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Ill

The ethmoid and the pneumatic sinuses.

The ethmoid and the pneumatic sinuses.

112

is a high, narrow aperture leading into the little larger, irregular
sinus 23 a' in the ventro-caudal part of the frontal bone, caudally
to the sinus IF. The sinus is elongated naso-dorsally over the
sinus IF and 21' and borders on the sinus 10 a'.

The sinus 25' is a very small sinus, not quite the size of a
pea, in the presphenoid, where it lies ventrally to the foramen
opticum, caudally to the sinus 23'.

The sinus 26' is a little larger irregular sinus, lying caudally
to the preceding, right under the foramen opticum.

The sinus V is a quite small sinus in the presphenoid. A
little ventrally to the aperture of the preceding sinus there is a
rather large aperture leading into a rather extensive sinus, the
sinus Va', pneumatizing the very largest part of the presphenoid.
It is divided into many small „cells" through bony lamellae which
are mostly arranged in frontal and sagittal planes. Through this
sinus the foramen opticum extends as a long and wide canal. Besides
the already mentioned pneumatic sinuses in the left half of
the presphenoid the sinus V a' in the right half expands also through
the septum downwards into the vomer and then further on into
the left side, where it is, however, only occupying the smaller part
of the presphenoid.

The sinus VII' is a very small sinus in the presphenoid.

Between the projecting rostral rim of the nasoturbinal and the
maxilloturbinal there is a long, furrow-shaped groove, of the breadth
of a finger, on the lateral wall of the nasal cavity, o: on the lateral
wall of the medial nasal passage. The bottom of this groove is
for the greater part formed by the lamina lateralis of the ethmoid;
only rostrad the maxillary and the intermaxillary take part in it.
Caudally in this groove and directly rostrad to the lamina lateralis
, between this latter and the downwards directed processus
of the nasoturbinal, there is a very large aperture leading into
a pneumatic sinus which is, judging from the situation of the
aperture, the sinus maxillaris. Through the aperture the way leads
into a broad and deep irregular compartment in the corpus of the
maxillary, where it reaches down to the alveolus of dps, and caudally
a little beyond the alveolus of dp4, and here it borders on
the sinus 10a'. The sinus maxillaris expands in different directions;
dorsally it extends upwards to the facial part of the maxillary,
where it forms several high but narrow compartments and continues
into the proc. zygomaticus, round the short but very wide
canalis infraorbitalis, i. e. this canal as usually runs through the
sinus maxillaris. The sinus extends rostrad, far forwards in the
corpus and the proc. palatinus in the shape of a long and rather
high compartment with a few larger sections. Finally the sinus
maxillaris expands upwards into the pars orbitalis of the frontale,
in the nasal part of which it torms a rather extensive multilocular
compartment, which is caudally bordering on the sinus 8 a' and
10 a', and ends in a dorsal expansion in the lacrymale in the shape
of a high and wide but very narrow compartment.

In the nasal end of the above mentioned furrow-shaped groove
there is a large aperture (1| cm high and \ cm broad) leading
into a large sinus intermaxillaris inferior which expands in the
largest part of the intermaxillare and reaches caudally upwards
into the pars ascendens where it borders on the sinus intermaxillaris
superior. The greater part of this sinus lies in the
corpus of the intermaxillare and is divided into several large
sections, but does not by far reach to the anterior end of the
intermaxillary bone.

Bostrally in the large diverticle of the mucous membrane, mentioned
p. 103, laterally to the cartilaginous part of the nasoturbinal,
there are two enormous apertures close side by side. The medial,
obliquely oval aperture, 5 cm high and 2 cm broad, lies in the
nasal bone close by the suture between this bone and the intermaxillare
. The appertinent sinus nasalis expands mainly in the
nasal bone, where it obtains a considerable depth (7 cm) and is
divided into a few rather large compartments. Laterally it breaks
through the suture between the nasale and the frontale, but is
only slightly expanded in the last-named bone, where it borders
on the sinus 6'. — The other, lateral, aperture lies in the intermaxillary
close before the suture between the nasale and the
intermaxillare and is 4 cm high and 1\ cm broad. The appertaining
sinus intermaxillaris superior is of only small circumference
; it is deep but very narrow and only rearches to the surface
of the intermaxillare between the sinus nasalis and the sinus
intermaxillaris inferior.

Finally there are some pneumatic sinuses issuing from the
cavum tympani. Through chiselling off the petrosum a great number
of relatively large apertures are seen on all the bottom of the
tympanicum, closely side by side, only separated by bony edges.
Each aperture leads to a sinus, a cellula tympanica. Some of
these numerous cellulse only are low pits, but most of them reach
to the surface of the tympanicum; of these latter the greater part
are quite small and only a few of them (3) have obtained a relatively
considerable size. Finally there is caudally in the tympanicum
a very large aperture of the breadth of a finger which
leads into a sinus occipitalis in the exoccipitale; this sinus consists
of a rather large compartment from which several smaller
compartments radiate towards the surface; together they pneuma-
tize a little more than the lateral half of the exoccipitale.

The right half of the same skull (PI. 29 figs. 1—2, PI. 43 figs.
1, 3, 4, PI. 45 fig. 1).

The system consists of the following pneumatic sinuses: sinus
Y, I" and V essentially as in the left side; only with the
exception that the sinus 1' is larger and raising from the bottom
of the sinus nasalis. The rostral part of the nasoturbinal is pneu-
matized and contains 3 sinuses. Most rostrad there is a relatively
large sinus, the aperture of which is placed in a depression
on the lateral wall of the nasal cavity, 1 cm ventrally to the nasoturbinal
. The sinus expands laterally and reaches to the surface
of the pars orbitalis of the frontale between the sinuses 4', 5' and
6 a'. The medial sinus, the aperture of which is placed a little
ventrally to the preceding, is narrow and ends laterally as a rather
large bulla rising from the bottom of the sinuses 4' and 6 a'. The
caudal, rather high but narrow sinus ends in an aperture exactly
ventrally to the nasoturbinal. The sinus 2' sends besides a prolongation
into the nasoturbinal (see below) between the rostral
and medial sinuses.

The sinus 2\ which is not found in the left side, is a small
sinus in the frontal bone which does not reach to the surface, as
it is covered by the sinus nasalis. It extends besides downwards
into the nasal part of the nasoturbinale.

The sinus 3' is a rather large sinus in the frontale, divided
into several smaller compartments. It occupies a rather considerable
part of the room which is in the left side occupied by
the sinus 6'.

The sinus 3 a', which is not found in the left side, is an
enormous sinus occupying the area which is in the left half pneu-
matized by the sinus 7', the medio-caudal part of the sinus 6',
the rostral part of the sinus 8', together with by far the greater
part of the sinus 9'. For a short distance in the frontale the
sinus 3' projects right into septum sinuum and here cuts off the
sinus 3 a' from reaching to the surface. As regards the system
of consolidating bony lamellae the matter is in the main the same
as in the sinus 7' of the left side.

The sinus 3 b' is a. little bulla rising from the bottom of the
sinus 3' and 4'.

The sinus 4-' has become a relatively large sinus, divided
into several smaller compartments, of which a single one reaches
to the surface of the frontale, rostrad to the sinus 3' and laterally
to the sinus intermaxillaris sup. et inf. The greater part of
the sinus 4' lies in the orbital part of the frontale, where it has
completely supplanted the sinus 8 a'; it continues caudally into
the pars temporalis of the frontal bone, but is here for the greater
part covered by the sinus 3 a'.

The sinus 5', which is not found in the left side, is a very
small sinus with two compartments in the medial wall of the orbit
, caudally to the sinus 6 a' and a sinus in the nasoturbinal.

The sinus 6' has, compared to the corresponding one of the
left side, been reduced to a very small sinus raising a little from
the bottom of the sinus 3 a'.

The sin us 6a\ which is considerably larger than that of the
left side, is a sinus of two compartments in the pars orbitalis of
the frontale, ventrally to the sinus 4', rostrad bordering on the
sinus maxillaris.